diff --git a/2021/input/2021/day14.txt b/2021/input/2021/day14.txt
new file mode 100644
index 0000000..55664c0
--- /dev/null
+++ b/2021/input/2021/day14.txt
@@ -0,0 +1,102 @@
+VHCKBFOVCHHKOHBPNCKO
+
+SO -> F
+OP -> V
+NF -> F
+BO -> V
+BH -> S
+VB -> B
+SV -> B
+BK -> S
+KC -> N
+SP -> O
+CP -> O
+VN -> O
+HO -> S
+PC -> B
+CS -> O
+PO -> K
+KF -> B
+BP -> K
+VO -> O
+HB -> N
+PH -> O
+FF -> O
+FB -> K
+CC -> H
+FK -> F
+HV -> P
+CO -> S
+OC -> N
+KV -> V
+SS -> O
+FC -> O
+NP -> B
+OH -> B
+OF -> K
+KB -> K
+BN -> C
+OK -> C
+NC -> O
+NO -> O
+FS -> C
+VP -> K
+KP -> S
+VS -> B
+VV -> N
+NN -> P
+KH -> P
+OB -> H
+HP -> H
+KK -> H
+FH -> F
+KS -> V
+BS -> V
+SN -> H
+CB -> B
+HN -> K
+SB -> O
+OS -> K
+BC -> H
+OV -> N
+PN -> B
+VH -> N
+SK -> C
+PV -> K
+VC -> N
+PF -> S
+NB -> B
+PP -> S
+NS -> F
+PB -> B
+CV -> C
+HK -> P
+PK -> S
+NH -> B
+SH -> V
+KO -> H
+NV -> B
+HH -> V
+FO -> O
+CK -> O
+VK -> F
+HF -> O
+BF -> C
+BV -> P
+KN -> K
+VF -> C
+FN -> V
+ON -> C
+SF -> F
+SC -> C
+OO -> S
+FP -> K
+PS -> C
+NK -> O
+BB -> V
+HC -> H
+FV -> V
+CH -> N
+HS -> V
+CF -> F
+CN -> S
diff --git a/2021/src/day14.rs b/2021/src/day14.rs
new file mode 100644
index 0000000..3797fad
--- /dev/null
+++ b/2021/src/day14.rs
@@ -0,0 +1,104 @@
+use std::{
+    collections::HashMap,
+    fmt::{Debug, Error, Formatter},
+    num::ParseIntError,
+    ops::{Index, IndexMut},
+    str::FromStr,
+};
+
+use anyhow::Result;
+use aoc_runner_derive::{aoc, aoc_generator};
+use thiserror::Error;
+
+fn expand(template: &[u8], rules: &HashMap<&[u8], u8>) -> Vec<u8> {
+    let mut res = vec![0u8; template.len() * 2 - 1];
+    template.windows(2).enumerate().for_each(|(i, xy)| {
+        let z = rules[xy];
+        res[i * 2] = xy[0];
+        res[i * 2 + 1] = z;
+        res[i * 2 + 2] = xy[1];
+    });
+    //dbg!(String::from_utf8_lossy(&res));
+    res
+}
+
+fn count(template: &[u8]) -> (usize, usize) {
+    let m = template
+        .iter()
+        .fold(HashMap::<u8, usize>::new(), |mut m, v| {
+            *m.entry(*v).or_insert(0) += 1;
+            m
+        });
+    m.values()
+        .fold((usize::MAX, 0), |(min, max), v| (min.min(*v), max.max(*v)))
+}
+
+#[aoc(day14, part1)]
+fn part1(input: &str) -> Result<usize> {
+    let (template, rules) = input.split_once("\n\n").unwrap();
+    let rules: HashMap<&[u8], u8> = rules
+        .lines()
+        .map(|l| {
+            let (pair, insert) = l.split_once(" -> ").unwrap();
+            (pair.as_bytes(), insert.as_bytes()[0])
+        })
+        .collect();
+    let mut template = template.as_bytes().to_vec();
+    for i in 1..11 {
+        template = expand(&template, &rules);
+        //println!("After step {}: {}", i, String::from_utf8_lossy(&template));
+    }
+    let (min, max) = count(&template);
+    Ok(max - min)
+}
+
+/*
+#[aoc(day14, part2)]
+fn part2(input: &[u64]) -> Result<u64> {
+todo!("part2");
+Ok(0)
+}
+*/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part1() -> Result<()> {
+        let input = r#"
+NNCB
+
+CH -> B
+HH -> N
+CB -> H
+NH -> C
+HB -> C
+HC -> B
+HN -> C
+NN -> C
+BH -> H
+NC -> B
+NB -> B
+BN -> B
+BB -> N
+BC -> B
+CC -> N
+CN -> C
+"#
+        .trim();
+        assert_eq!(part1(input)?, 1588);
+        Ok(())
+    }
+
+    /*
+    #[test]
+    fn test_part2()->Result<()> {
+    let input = r#"
+    "#
+    .trim();
+    assert_eq!(part2(&parse(input)?)?, u64::MAX);
+    Ok(())
+    }
+    */
+}
diff --git a/2021/src/lib.rs b/2021/src/lib.rs
index b37d517..8f95c8a 100644
--- a/2021/src/lib.rs
+++ b/2021/src/lib.rs
@@ -2,6 +2,7 @@ pub mod day1;
 pub mod day10;
 pub mod day11;
 pub mod day12;
+pub mod day14;
 pub mod day2;
 pub mod day3;
 pub mod day4;