diff --git a/2021/Cargo.lock b/2021/Cargo.lock
index 145cf10..243822b 100644
--- a/2021/Cargo.lock
+++ b/2021/Cargo.lock
@@ -22,6 +22,7 @@ name = "advent-2021"
 version = "0.1.0"
 dependencies = [
  "color-eyre",
+ "num",
 ]
 
 [[package]]
@@ -134,6 +135,82 @@ dependencies = [
  "autocfg",
 ]
 
+[[package]]
+name = "num"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "43db66d1170d347f9a065114077f7dccb00c1b9478c89384490a3425279a4606"
+dependencies = [
+ "num-bigint",
+ "num-complex",
+ "num-integer",
+ "num-iter",
+ "num-rational",
+ "num-traits",
+]
+
+[[package]]
+name = "num-bigint"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f93ab6289c7b344a8a9f60f88d80aa20032336fe78da341afc91c8a2341fc75f"
+dependencies = [
+ "autocfg",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-complex"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "26873667bbbb7c5182d4a37c1add32cdf09f841af72da53318fdb81543c15085"
+dependencies = [
+ "num-traits",
+]
+
+[[package]]
+name = "num-integer"
+version = "0.1.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2cc698a63b549a70bc047073d2949cce27cd1c7b0a4a862d08a8031bc2801db"
+dependencies = [
+ "autocfg",
+ "num-traits",
+]
+
+[[package]]
+name = "num-iter"
+version = "0.1.42"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b2021c8337a54d21aca0d59a92577a029af9431cb59b909b03252b9c164fad59"
+dependencies = [
+ "autocfg",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-rational"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d41702bd167c2df5520b384281bc111a4b5efcf7fbc4c9c222c815b07e0a6a6a"
+dependencies = [
+ "autocfg",
+ "num-bigint",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a64b1ec5cda2586e284722486d802acf1f7dbdc623e2bfc57e65ca1cd099290"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "object"
 version = "0.27.1"
diff --git a/2021/Cargo.toml b/2021/Cargo.toml
index 7cacf6e..b493610 100644
--- a/2021/Cargo.toml
+++ b/2021/Cargo.toml
@@ -7,4 +7,5 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-color-eyre = "^0.5.11"
\ No newline at end of file
+color-eyre = "^0.5.11"
+num = "^0.4.0"
\ No newline at end of file
diff --git a/2021/src/day5.rs b/2021/src/day5.rs
new file mode 100644
index 0000000..53dbca1
--- /dev/null
+++ b/2021/src/day5.rs
@@ -0,0 +1,77 @@
+use color_eyre::eyre;
+use num::{Integer, integer::gcd};
+
+
+#[derive(Copy, Clone)]
+struct Point {
+    x: isize,
+    y: isize,
+}
+
+
+#[derive(Copy, Clone)]
+struct Line {
+    start: Point,
+    end: Point,
+}
+
+
+#[derive(Copy, Clone)]
+struct Slope {
+    rise: isize,
+    run: isize,
+}
+
+
+impl Line {
+    fn slope(&self) -> Slope {
+        let mut rise = self.end.y - self.start.y;
+        let mut run = self.end.x - self.start.x;
+        if rise != 0 && run != 0 {
+            let divisor = gcd(rise, run);
+            rise /= divisor;
+            run /= divisor;
+        }
+        Slope {rise, run}
+    }
+}
+
+
+struct PointsIter<'a> {
+    line: &'a Line,
+    pos: Point,
+    slope: Slope,
+}
+
+impl PointsIter<'_> {
+    fn from(line: &Line) -> Self {
+        PointsIter {
+            line,
+            pos: line.start,
+            slope: line.slope(),
+        }
+    }
+}
+
+impl Iterator for PointsIter {
+    type Item = Point;
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.pos.x = self.line.start.x && self.pos.y == self.line.start.y {
+            return Some(self.pos);
+        }
+
+        if self.pos.x != self.line.end.x && self.pos.y != self.line.end.y {
+            self.pos.y += self.slope.rise;
+            self.pos.x += self.slope.run;
+            return Some(self.pos);
+        }
+        else {
+            return None;
+        }
+    }
+}
+
+
+struct GridCounter<const W: usize, const H: usize> {
+    rows: [[usize; W]; H],
+}