diff --git a/day4/Cargo.lock b/day4/Cargo.lock
new file mode 100644
index 0000000..e92c02c
--- /dev/null
+++ b/day4/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day4"
+version = "0.1.0"
diff --git a/day4/Cargo.toml b/day4/Cargo.toml
new file mode 100644
index 0000000..8842130
--- /dev/null
+++ b/day4/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day4"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day4/src/main.rs b/day4/src/main.rs
new file mode 100644
index 0000000..102cf85
--- /dev/null
+++ b/day4/src/main.rs
@@ -0,0 +1,74 @@
+use std::collections::HashMap;
+
+fn main() {
+    let input = include_str!("../input.txt");
+
+    let mut scores = vec![];
+    let mut scratchcards: HashMap<usize, usize> = HashMap::new();
+
+    let mut index = 0;
+
+    for card in input.split('\n') {
+        if card == "" {
+            continue;
+        }
+
+        index += 1;
+
+        let data = card.split(": ").collect::<Vec<_>>()[1];
+
+        let [ winner_str, our_str ] = data.split('|').collect::<Vec<_>>()[..] else { panic!("Invalid card") };
+
+        let mut winners: Vec<u8> = vec![];
+        let mut ours: Vec<u8> = vec![];
+
+        for num in winner_str.split(' ') {
+            if num.is_empty() {
+                continue;  // there are some double-spaces in the cards
+            }
+
+            winners.push(num.parse().unwrap());
+        }
+
+        println!("- the winning numbers are {:?}", winners);
+
+        for num in our_str.split(' ') {
+            if num.is_empty() {
+                continue;  // there are some double-spaces in the cards
+            }
+
+            ours.push(num.parse().unwrap());
+        }
+
+        println!("- our numbers are {:?}", ours);
+
+        let mut n = 0;
+        for num in ours {
+            if winners.contains(&num) {
+                println!("  - {} is a winner!", num);
+                n += 1
+            }
+        }
+
+        if n != 0 {
+            let score = 2_usize.pow(n - 1);
+            scores.push(score);
+            println!("Card {} has {} winning numbers, scoring it {} points!", index, n, score);
+
+            let factor = scratchcards.get(&index).unwrap_or(&0) + 1;
+            println!("- Adding {} cards to each of the next {} numbers", factor, n);
+            for i in index+1..index + 1 + TryInto::<usize>::try_into(n).unwrap() {
+                let old_copies = scratchcards.get(&i).unwrap_or(&0);
+                println!("  - Adding {} cards to the {} that were already in card {}", factor, old_copies, i);
+                scratchcards.insert(i, old_copies + factor);
+            }
+        } else {
+            println!("This card didn't win at all, better luck next time...");
+        }
+    }
+
+    println!("The total score was {}", scores.iter().sum::<usize>());
+
+    let clones: usize = scratchcards.into_values().sum();
+    println!("You have {} scratchcard clones, plus the original {}, which leaves you with a total of {}", clones, index, clones + index);
+}