diff --git a/2022/inputs/25.txt b/2022/inputs/25.txt
new file mode 100644
index 0000000..b4737fe
--- /dev/null
+++ b/2022/inputs/25.txt
@@ -0,0 +1,126 @@
+2=1
+2=-02211=
+2=-1111=2-0-20=
+2=2-=12
+1--2-=2211-221
+1=20011
+1221=021-0=2011-1
+1=00=202011=
+200=121-=2-11=21
+2-21002021202
+1-11=12011112
+1==2-=0-=2-0-0
+20=-12--12
+101122=222021221-
+12=2200-1==1=12=1=1
+2==-21=-=2
+1==-1222-1==2-
+111-2-2=0
+1=2
+1=20=-00=22
+1=2=0-2101=2
+10=
+10-=12101-102=1=
+12=11=-
+1202=0--0-2==0
+1-0--
+10210210-10021=2-2
+22=
+12-110101
+2=-===0=0=11--
+2=21022-00-
+2-111102102--201=0
+2=-2=
+12=22=11-1000=121
+11=10-02111211
+20210121--0=1=-=
+1=-
+10=-==02-20-0=01
+21=0=-=
+2=10002
+1-0102-020201121
+11---01101=--
+1=-1=-=-011
+211-00-2==21==
+21
+1201-1202=2-0
+21000=2=1-=10--2
+1=0=
+1-1
+1-2---=1====-0210=-0
+2-220-=
+122-
+110200-0
+2=--2
+20112=0-2022-
+1=-0--
+1=-01-0-10=2=0===-
+1=22=2=--11=-0-2111
+1==00-1=00=0-
+1=2212-1-=201
+2-200=2001
+2222012-10-0=-0=
+1-====
+100=2200
+1-11==0
+1--2111-1
+1---2121-202210=2
+11222=
+1=2102-2221-111-
+111
+1=
+1--0=-1
+10=00=10=---1=-
+1=0==-2
+220002
+1==211-0=222102-
+1-==-121021
+1202-1=01--202
+12=-0===11=0
+20-001=
+1000-2-==2=-
+1=01--
+10=--01221
+1-=2-=0=-0==10-22-
+2021212-1020=002
+11===1==-2-01-21
+2-00-10-
+12-0221212000
+201==
+20011
+2---0=1222--02
+20-
+10-=02010
+101--0202=-2=1==01
+2=0121-02112-0=
+2-=-=1011
+11-=02
+110-2001
+1==011-12000101-11
+2=
+1-11-=--=
+110
+101=21
+1=11
+212-10020-212111-2
+102=22
+1-
+1-02=22-=1==2
+11=10-00-=00-00=-
+220200-=2
+1-0=----
+1022=0-2--==--1
+1-=201-1021
+2=-1-10=1=-2020=00
+12201=0102-0110=-
+20=2
+2020=-===1==-212
+1=0-222-2=22=-=
+1=--12==0100=-21
+1=1-2
+1=-220001=1
+20
+1=1
+1=0=-=1=0-=01
+202102-200
+2-=2-110012
diff --git a/2022/src/day25.rs b/2022/src/day25.rs
index 8c045e4..c09aa38 100644
--- a/2022/src/day25.rs
+++ b/2022/src/day25.rs
@@ -1,5 +1,71 @@
 use anyhow::Result;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+fn parse_num(num: &[u8]) -> Result<i64> {
+    let mut total = 0;
+    let mut factor = 1;
+
+    for &b in num.iter().rev() {
+        match b {
+            b'0' => (),
+            b'1' => total += factor,
+            b'2' => total += 2 * factor,
+            b'-' => total -= factor,
+            b'=' => total -= 2 * factor,
+            other => anyhow::bail!("Invalid digit {other}"),
+        }
+
+        factor *= 5;
+    }
+
+    Ok(total)
+}
+
+fn encode(mut num: i64) -> String {
+    let mut buffer = Vec::new();
+
+    while num > 0 {
+        match num % 5 {
+            0 => buffer.push(b'0'),
+            1 => buffer.push(b'1'),
+            2 => buffer.push(b'2'),
+            3 => {
+                buffer.push(b'=');
+                num += 2
+            }
+            4 => {
+                buffer.push(b'-');
+                num += 1;
+            }
+            _ => unreachable!("math"),
+        }
+
+        num /= 5;
+    }
+
+    // We've built the string right to left, to print we must reverse
+    buffer.reverse();
+
+    // Safe unwrap as we've only pushed valid ascii characters
+    String::from_utf8(buffer).unwrap()
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let total = input
+        .split(|&b| b == b'\n')
+        .map(parse_num)
+        .try_fold(0, |acc, val| val.map(|val| val + acc))?;
+
+    Ok(encode(total))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("./samples/25.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "2=-1=0");
+    }
 }
diff --git a/2022/src/samples/25.txt b/2022/src/samples/25.txt
new file mode 100644
index 0000000..027aeec
--- /dev/null
+++ b/2022/src/samples/25.txt
@@ -0,0 +1,13 @@
+1=-0-2
+12111
+2=0=
+21
+2=01
+111
+20012
+112
+1=-1=
+1-12
+12
+1=
+122