diff --git a/input/day3.txt b/input/day3.txt
new file mode 100644
index 0000000..1d938ed
--- /dev/null
+++ b/input/day3.txt
@@ -0,0 +1,1000 @@
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diff --git a/src/day3.rs b/src/day3.rs
new file mode 100644
index 0000000..89342e1
--- /dev/null
+++ b/src/day3.rs
@@ -0,0 +1,87 @@
+pub fn day3() {
+    // let input = r#"
+    // 00100
+    // 11110
+    // 10110
+    // 10111
+    // 10101
+    // 01111
+    // 00111
+    // 11100
+    // 10000
+    // 11001
+    // 00010
+    // 01010
+    //     "#;
+    let input = include_str!("../input/day3.txt");
+
+    let numbers: Vec<u32> = input
+        .trim()
+        .lines()
+        .map(|l| u32::from_str_radix(l.trim(), 2).unwrap())
+        .collect();
+    let nbits = input.trim().lines().next().unwrap().trim().len();
+
+    let gamma = gamma(&numbers);
+    println!("gamma: {}", gamma);
+    println!("epsilon: {}", epsilon(gamma, nbits));
+
+    println!("oxygen: {}", oxygen(&numbers, nbits));
+    println!("co2: {}", co2(&numbers, nbits));
+}
+
+fn gamma(numbers: &[u32]) -> u32 {
+    let mut gamma: u32 = 0;
+    for i in 0..32 {
+        gamma = gamma | (most_common_bit(numbers, i) << i);
+    }
+    gamma
+}
+
+fn most_common_bit(numbers: &[u32], pos: u32) -> u32 {
+    let count = numbers.iter().filter(|&n| (n >> pos) & 1 == 1).count();
+    let frac = (count as f32) / (numbers.len() as f32);
+    frac.round() as u32
+}
+
+fn epsilon(gamma: u32, nbits: usize) -> u32 {
+    println!("{:#b}", !gamma);
+    println!("{:#b}", 2_u32.pow(nbits as u32) - 1);
+    !gamma & ((1 << nbits) - 1)
+}
+
+fn oxygen(numbers: &[u32], nbits: usize) -> u32 {
+    let mut vec: Vec<u32> = numbers.into();
+    let mut bit: u32 = nbits as u32;
+    while vec.len() != 1 {
+        bit -= 1;
+        let most_common = most_common_bit(&vec, bit);
+        vec = vec
+            .into_iter()
+            .filter(|n| ((n >> bit) & 1) == most_common)
+            .collect();
+        for n in vec.iter() {
+            print!("{:#b}, ", n);
+        }
+        println!();
+    }
+    *vec.get(0).unwrap()
+}
+
+fn co2(numbers: &[u32], nbits: usize) -> u32 {
+    let mut vec: Vec<u32> = numbers.into();
+    let mut bit: u32 = nbits as u32;
+    while vec.len() != 1 {
+        bit -= 1;
+        let least_common = 1 - most_common_bit(&vec, bit);
+        vec = vec
+            .into_iter()
+            .filter(|n| ((n >> bit) & 1) == least_common)
+            .collect();
+        // for n in vec.iter() {
+        //     print!("{:#b}, ", n);
+        // }
+        // println!();
+    }
+    *vec.get(0).unwrap()
+}
diff --git a/src/main.rs b/src/main.rs
index ce49bb9..06ffbba 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,7 +2,8 @@
 
 mod day1;
 mod day2;
+mod day3;
 
 fn main() {
-    day2::day2();
+    day3::day3();
 }