diff --git a/aoc2019/input/day05.txt b/aoc2019/input/day05.txt
new file mode 100644
index 0000000..c6d4caf
--- /dev/null
+++ b/aoc2019/input/day05.txt
@@ -0,0 +1 @@
+3,225,1,225,6,6,1100,1,238,225,104,0,1101,90,60,224,1001,224,-150,224,4,224,1002,223,8,223,1001,224,7,224,1,224,223,223,1,57,83,224,1001,224,-99,224,4,224,1002,223,8,223,1001,224,5,224,1,223,224,223,1102,92,88,225,101,41,187,224,1001,224,-82,224,4,224,1002,223,8,223,101,7,224,224,1,224,223,223,1101,7,20,225,1101,82,64,225,1002,183,42,224,101,-1554,224,224,4,224,102,8,223,223,1001,224,1,224,1,224,223,223,1102,70,30,224,101,-2100,224,224,4,224,102,8,223,223,101,1,224,224,1,224,223,223,2,87,214,224,1001,224,-2460,224,4,224,1002,223,8,223,101,7,224,224,1,223,224,223,102,36,180,224,1001,224,-1368,224,4,224,1002,223,8,223,1001,224,5,224,1,223,224,223,1102,50,38,225,1102,37,14,225,1101,41,20,225,1001,217,7,224,101,-25,224,224,4,224,1002,223,8,223,101,2,224,224,1,224,223,223,1101,7,30,225,1102,18,16,225,4,223,99,0,0,0,677,0,0,0,0,0,0,0,0,0,0,0,1105,0,99999,1105,227,247,1105,1,99999,1005,227,99999,1005,0,256,1105,1,99999,1106,227,99999,1106,0,265,1105,1,99999,1006,0,99999,1006,227,274,1105,1,99999,1105,1,280,1105,1,99999,1,225,225,225,1101,294,0,0,105,1,0,1105,1,99999,1106,0,300,1105,1,99999,1,225,225,225,1101,314,0,0,106,0,0,1105,1,99999,7,226,226,224,102,2,223,223,1006,224,329,101,1,223,223,1107,677,226,224,102,2,223,223,1006,224,344,1001,223,1,223,8,677,226,224,1002,223,2,223,1005,224,359,101,1,223,223,107,677,677,224,1002,223,2,223,1006,224,374,101,1,223,223,7,677,226,224,1002,223,2,223,1006,224,389,101,1,223,223,108,677,226,224,1002,223,2,223,1005,224,404,101,1,223,223,1108,677,226,224,102,2,223,223,1005,224,419,101,1,223,223,8,226,677,224,102,2,223,223,1006,224,434,1001,223,1,223,1008,677,677,224,1002,223,2,223,1005,224,449,1001,223,1,223,1107,226,677,224,102,2,223,223,1006,224,464,101,1,223,223,107,226,677,224,1002,223,2,223,1006,224,479,1001,223,1,223,7,226,677,224,102,2,223,223,1005,224,494,1001,223,1,223,8,677,677,224,102,2,223,223,1006,224,509,1001,223,1,223,1108,677,677,224,102,2,223,223,1005,224,524,1001,223,1,223,1108,226,677,224,1002,223,2,223,1005,224,539,101,1,223,223,107,226,226,224,102,2,223,223,1006,224,554,1001,223,1,223,1007,226,226,224,102,2,223,223,1005,224,569,1001,223,1,223,1008,226,226,224,102,2,223,223,1005,224,584,101,1,223,223,1007,677,677,224,1002,223,2,223,1005,224,599,1001,223,1,223,108,677,677,224,1002,223,2,223,1006,224,614,1001,223,1,223,1007,226,677,224,1002,223,2,223,1006,224,629,101,1,223,223,1008,677,226,224,102,2,223,223,1005,224,644,101,1,223,223,1107,226,226,224,1002,223,2,223,1005,224,659,1001,223,1,223,108,226,226,224,1002,223,2,223,1005,224,674,101,1,223,223,4,223,99,226
diff --git a/aoc2019/src/day05.rs b/aoc2019/src/day05.rs
new file mode 100644
index 0000000..4a291b9
--- /dev/null
+++ b/aoc2019/src/day05.rs
@@ -0,0 +1,222 @@
+use aoc::err;
+use aoc::Result;
+
+const INPUT: &str = include_str!("../input/day05.txt");
+
+pub fn run() -> Result<()> {
+    println!("part 1: {}", part1(INPUT)?);
+    Ok(())
+}
+
+fn part1(input: &str) -> Result<i64> {
+    let mut intcode = Intcode::new(input)?;
+    intcode.add_input(1);
+    intcode.run()?;
+    intcode
+        .get_output()
+        .ok_or_else(|| err!("intcode gave no output"))
+}
+
+enum Parameter {
+    Position(usize),
+    Immediate(i64),
+}
+
+impl Parameter {
+    fn new(mode: i64, val: Option<&i64>) -> Result<Self> {
+        let val = *val.ok_or_else(|| err!("parameter value out of bounds"))?;
+        let mode = mode % 10;
+
+        match mode {
+            0 => {
+                if val < 0 {
+                    Err(err!("negative value for position parameter: {}", val))
+                } else {
+                    let val = val as usize;
+                    Ok(Parameter::Position(val))
+                }
+            }
+            1 => Ok(Parameter::Immediate(val)),
+            _ => Err(err!("wrong mode for parameter: {}", mode)),
+        }
+    }
+
+    fn get(&self, memory: &[i64]) -> Option<i64> {
+        match self {
+            Parameter::Position(address) => memory.get(*address).map(|v| *v),
+            Parameter::Immediate(value) => Some(*value),
+        }
+    }
+
+    fn set(&self, memory: &mut [i64], value: i64) -> Result<()> {
+        match self {
+            Parameter::Position(address) => {
+                let cell = memory
+                    .get_mut(*address)
+                    .ok_or_else(|| err!("memory write out of bounds"))?;
+                *cell = value;
+                Ok(())
+            }
+            Parameter::Immediate(_) => Err(err!("cannot write to immediate parameter")),
+        }
+    }
+}
+
+enum Opcode {
+    Add(Parameter, Parameter, Parameter),
+    Multiply(Parameter, Parameter, Parameter),
+    Input(Parameter),
+    Output(Parameter),
+    Halt,
+}
+
+struct Intcode {
+    memory: Vec<i64>,
+    input: Vec<i64>,
+    output: Vec<i64>,
+    ip: usize,
+}
+
+impl Intcode {
+    fn new(input: &str) -> Result<Self> {
+        let memory = input
+            .trim_end()
+            .split(',')
+            .map(|x| x.parse().map_err(|e| err!("couldn't parse int: {}", e)))
+            .collect::<Result<Vec<i64>>>()?;
+
+        Ok(Intcode {
+            memory,
+            input: Vec::new(),
+            output: Vec::new(),
+            ip: 0,
+        })
+    }
+
+    fn add_input(&mut self, value: i64) {
+        self.input.push(value);
+    }
+
+    fn get_opcode(&self) -> Result<Opcode> {
+        let instruction = self.memory[self.ip];
+
+        let opcode = instruction % 100;
+        match opcode {
+            1 => {
+                let op1 = Parameter::new(instruction / 100, self.memory.get(self.ip + 1))?;
+                let op2 = Parameter::new(instruction / 1000, self.memory.get(self.ip + 2))?;
+                let dst = Parameter::new(instruction / 10000, self.memory.get(self.ip + 3))?;
+
+                if let Parameter::Immediate(_) = dst {
+                    Err(err!("add: destination parameter can't be immediate"))
+                } else {
+                    Ok(Opcode::Add(op1, op2, dst))
+                }
+            }
+            2 => {
+                let op1 = Parameter::new(instruction / 100, self.memory.get(self.ip + 1))?;
+                let op2 = Parameter::new(instruction / 1000, self.memory.get(self.ip + 2))?;
+                let dst = Parameter::new(instruction / 10000, self.memory.get(self.ip + 3))?;
+
+                if let Parameter::Immediate(_) = dst {
+                    Err(err!("multiply: destination parameter can't be immediate"))
+                } else {
+                    Ok(Opcode::Multiply(op1, op2, dst))
+                }
+            }
+            3 => {
+                let dst = Parameter::new(instruction / 100, self.memory.get(self.ip + 1))?;
+
+                if let Parameter::Immediate(_) = dst {
+                    Err(err!("input: destination parameter can't be immediate"))
+                } else {
+                    Ok(Opcode::Input(dst))
+                }
+            }
+            4 => {
+                let op = Parameter::new(instruction / 100, self.memory.get(self.ip + 1))?;
+
+                Ok(Opcode::Output(op))
+            }
+            99 => Ok(Opcode::Halt),
+            _ => Err(err!("unknown opcode: {}", opcode)),
+        }
+    }
+
+    fn run(&mut self) -> Result<()> {
+        loop {
+            if self.ip >= self.memory.len() {
+                return Err(err!("reached end of program without halting"));
+            }
+
+            let opcode = self.get_opcode()?;
+
+            match opcode {
+                Opcode::Add(op1, op2, dst) => {
+                    let val1 = op1
+                        .get(&self.memory)
+                        .ok_or_else(|| err!("add: op1 out of bounds"))?;
+                    let val2 = op2
+                        .get(&self.memory)
+                        .ok_or_else(|| err!("add: op1 out of bounds"))?;
+
+                    dst.set(&mut self.memory, val1 + val2)?;
+
+                    self.ip += 4;
+                }
+                Opcode::Multiply(op1, op2, dst) => {
+                    let val1 = op1
+                        .get(&self.memory)
+                        .ok_or_else(|| err!("add: op1 out of bounds"))?;
+                    let val2 = op2
+                        .get(&self.memory)
+                        .ok_or_else(|| err!("add: op1 out of bounds"))?;
+
+                    dst.set(&mut self.memory, val1 * val2)?;
+
+                    self.ip += 4;
+                }
+                Opcode::Input(dst) => {
+                    let input = self
+                        .input
+                        .pop()
+                        .ok_or_else(|| err!("tried to read input but it was empty"))?;
+                    dst.set(&mut self.memory, input)?;
+
+                    self.ip += 2;
+                }
+                Opcode::Output(op) => {
+                    let val = op
+                        .get(&self.memory)
+                        .ok_or_else(|| err!("output: op out of bounds"))?;
+                    self.output.push(val);
+
+                    self.ip += 2;
+                }
+                Opcode::Halt => break Ok(()),
+            }
+        }
+    }
+
+    fn get_output(&self) -> Option<i64> {
+        for (i, out) in self.output.iter().enumerate() {
+            if i < self.output.len() - 1 {
+                assert_eq!(*out, 0);
+            } else {
+                return Some(*out);
+            }
+        }
+
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 16225258);
+    }
+}
diff --git a/aoc2019/src/lib.rs b/aoc2019/src/lib.rs
index e051fbd..f290640 100644
--- a/aoc2019/src/lib.rs
+++ b/aoc2019/src/lib.rs
@@ -2,3 +2,4 @@ pub mod day01;
 pub mod day02;
 pub mod day03;
 pub mod day04;
+pub mod day05;
diff --git a/aoc2019/src/main.rs b/aoc2019/src/main.rs
index 4fa0ab4..c4ec62b 100644
--- a/aoc2019/src/main.rs
+++ b/aoc2019/src/main.rs
@@ -4,9 +4,10 @@ use aoc2019::day01;
 use aoc2019::day02;
 use aoc2019::day03;
 use aoc2019::day04;
+use aoc2019::day05;
 
 fn main() -> Result<()> {
-    let days: &[fn() -> Result<()>] = &[day01::run, day02::run, day03::run, day04::run];
+    let days: &[fn() -> Result<()>] = &[day01::run, day02::run, day03::run, day04::run, day05::run];
 
     aoc::run(days)
 }