diff --git a/2019/12/Cargo.toml b/2019/12/Cargo.toml
new file mode 100644
index 0000000..13abe5d
--- /dev/null
+++ b/2019/12/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "day12"
+version = "0.1.0"
+authors = ["kageru <kageru@encode.moe>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+scan_fmt = "0.2.4"
diff --git a/2019/12/input b/2019/12/input
new file mode 100644
index 0000000..f588984
--- /dev/null
+++ b/2019/12/input
@@ -0,0 +1,4 @@
+<x=1, y=-4, z=3>
+<x=-14, y=9, z=-4>
+<x=-4, y=-6, z=7>
+<x=6, y=-9, z=-11>
diff --git a/2019/12/src/main.rs b/2019/12/src/main.rs
new file mode 100644
index 0000000..b5515ad
--- /dev/null
+++ b/2019/12/src/main.rs
@@ -0,0 +1,63 @@
+#[macro_use]
+extern crate scan_fmt;
+
+#[derive(Debug, PartialEq, Eq)]
+struct Moon {
+    x: i32,
+    y: i32,
+    z: i32,
+    x_vel: i32,
+    y_vel: i32,
+    z_vel: i32,
+}
+
+fn main() {
+    println!("Hello, world!");
+}
+
+fn gcd(mut x: u32, mut y: u32) -> u32 {
+    let mut remainder;
+    while y != 0 {
+        remainder = x % y;
+        x = y;
+        y = remainder;
+    }
+    x
+}
+
+fn lcm(x: u32, y: u32) -> u32 {
+    x * y / gcd(x, y)
+}
+
+#[rustfmt::skip]
+fn parse(line: &str) -> Moon {
+    let (x, y, z) = scan_fmt!(line, "<x={}, y={}, z={}>", i32, i32, i32).unwrap();
+    Moon { x, y, z, x_vel: 0, y_vel: 0, z_vel: 0, }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_gcd() {
+        assert_eq!(gcd(20, 10), 10);
+        assert_eq!(gcd(20, 15), 5);
+        assert_eq!(gcd(15, 20), 5);
+    }
+
+    #[test]
+    fn test_lcm() {
+        assert_eq!(lcm(20, 10), 20);
+        assert_eq!(lcm(3, 7), 21);
+        assert_eq!(lcm(7, 3), 21);
+        assert_eq!(lcm(lcm(7, 3), 5), 105);
+    }
+
+    #[test]
+    #[rustfmt::skip]
+    fn test_parse() {
+        assert_eq!(parse("<x=-14, y=9, z=-4>"), Moon { x: -14, y: 9, z: -4, x_vel: 0, y_vel: 0, z_vel: 0 });
+        assert_ne!(parse("<x=-14, y=9, z=-4>"), Moon { x: 14, y: 9, z: -4, x_vel: 0, y_vel: 0, z_vel: 0 });
+    }
+}