diff --git a/src/bin/day03.rs b/src/bin/day03.rs
index e3dfb05..1eb4150 100644
--- a/src/bin/day03.rs
+++ b/src/bin/day03.rs
@@ -1,8 +1,10 @@
-use color_eyre::{
-    eyre::{bail, ensure},
-    Result,
+use {
+    color_eyre::{
+        eyre::{bail, ensure},
+        Result,
+    },
+    std::{cell::Cell, collections::HashMap, io::stdin, rc::Rc},
 };
-use std::{cell::Cell, collections::HashMap, io::stdin, rc::Rc};
 
 #[derive(Clone, Copy)]
 struct SliceCols<'a, T> {
diff --git a/src/bin/day04.rs b/src/bin/day04.rs
new file mode 100644
index 0000000..b94a991
--- /dev/null
+++ b/src/bin/day04.rs
@@ -0,0 +1,36 @@
+use {color_eyre::eyre::ContextCompat, color_eyre::Result, std::io::stdin};
+
+fn main() -> Result<()> {
+    Ok(println!(
+        "{}",
+        stdin()
+            .lines()
+            .map(|ln| -> Result<_> {
+                let ln = ln?;
+                let (winning, nums) = ln
+                    .split_once(':')
+                    .context("Invalid record: missing ':' separator")?
+                    .1
+                    .split_once('|')
+                    .context("Invalid record: missing '|' separator")?;
+
+                let winning = winning
+                    .split_whitespace()
+                    .map(str::parse)
+                    .collect::<Result<Box<[u64]>, _>>()?;
+
+                let n = nums
+                    .split_whitespace()
+                    .map(str::parse)
+                    .map(|item| item.map(|item| winning.contains(&item)))
+                    .try_fold::<_, _, Result<_>>(0, |acc, x| Ok(acc + x? as u64))?;
+
+                if n != 0 {
+                    Ok(2_u64.pow(u32::try_from(n)?.saturating_sub(1)))
+                } else {
+                    Ok(0)
+                }
+            })
+            .try_fold::<_, _, Result<_>>(0, |acc, x| Ok(acc + x?))?
+    ))
+}