diff --git a/day04/Cargo.lock b/day04/Cargo.lock
new file mode 100644
index 0000000..b8f9a18
--- /dev/null
+++ b/day04/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day04"
+version = "0.1.0"
diff --git a/day04/Cargo.toml b/day04/Cargo.toml
new file mode 100644
index 0000000..0e45553
--- /dev/null
+++ b/day04/Cargo.toml
@@ -0,0 +1,4 @@
+[package]
+name = "day04"
+version = "0.1.0"
+edition = "2021"
diff --git a/day04/src/main.rs b/day04/src/main.rs
new file mode 100644
index 0000000..01e2221
--- /dev/null
+++ b/day04/src/main.rs
@@ -0,0 +1,61 @@
+use std::collections::{HashMap, HashSet};
+use std::io::{stdin, BufRead};
+
+fn main() {
+    let input = stdin().lock().lines().map(|l| l.unwrap());
+    let mut total_score = 0;
+    let mut card_counts = HashMap::new();
+    let mut total_single_cards = 0;
+
+    for (id, line) in input.enumerate() {
+        let card = line.split_once(':').unwrap().1;
+        let (entries, winners) = card.split_once('|').unwrap();
+
+        let entset = entries
+            .trim()
+            .split(' ')
+            .filter(|num| !num.is_empty())
+            .collect::<HashSet<_>>();
+        let winset = winners
+            .trim()
+            .split(' ')
+            .filter(|num| !num.is_empty())
+            .collect::<HashSet<_>>();
+
+        let common = entset.intersection(&winset);
+        let num_in_common = common.count();
+        total_score += to_score(num_in_common);
+
+        let repeat_count = card_counts.get(&(id + 1)).unwrap_or(&0).to_owned();
+
+        let r = to_range(id, num_in_common);
+        for win_card_copy in r {
+            let current_count = card_counts.get(&win_card_copy).unwrap_or(&0);
+            card_counts.insert(win_card_copy, current_count + 1 + repeat_count);
+        }
+
+        total_single_cards = id + 1;
+    }
+
+    let card_total = card_counts.iter().fold(0, |total, count| total + count.1);
+
+    println!(
+        "P1: {} P2: {}",
+        total_score,
+        total_single_cards + card_total
+    );
+}
+
+fn to_range(id: usize, win_count: usize) -> std::ops::Range<usize> {
+    let start = id + 2;
+    let end = start + win_count;
+    start..end
+}
+
+fn to_score(entries: usize) -> usize {
+    if entries == 0 {
+        0
+    } else {
+        1 << (entries - 1)
+    }
+}