diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index 43e3f1c..96dd0ff 100644
--- a/.gitea/workflows/build_and_run.yml
+++ b/.gitea/workflows/build_and_run.yml
@@ -11,7 +11,7 @@ jobs:
     name: Challenge for day
     strategy:
       matrix:
-        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
+        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day13/Cargo.toml b/day13/Cargo.toml
new file mode 100644
index 0000000..adb45f4
--- /dev/null
+++ b/day13/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day13"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day13/src/main.rs b/day13/src/main.rs
new file mode 100644
index 0000000..990e1dd
--- /dev/null
+++ b/day13/src/main.rs
@@ -0,0 +1,80 @@
+use std::{env, fs};
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> Vec<((i64, i64, i64), (i64, i64, i64))> {
+    let mut equations = Vec::new();
+    let mut equation = ((0, 0, 0), (0, 0, 0));
+    for (row, line) in input.lines().filter(|line| !line.is_empty()).enumerate() {
+        let pos = row % 3;
+        let tuple;
+        if pos == 0 || pos == 1 {
+            tuple = line[12..].split_once(", Y+").unwrap();
+        } else {
+            tuple = line[9..].split_once(", Y=").unwrap();
+        }
+
+        match pos {
+            0 => {
+                equation.0 .0 = tuple.0.parse().unwrap();
+                equation.1 .0 = tuple.1.parse().unwrap();
+            }
+            1 => {
+                equation.0 .1 = tuple.0.parse().unwrap();
+                equation.1 .1 = tuple.1.parse().unwrap();
+            }
+            _ => {
+                equation.0 .2 = tuple.0.parse().unwrap();
+                equation.1 .2 = tuple.1.parse().unwrap();
+            }
+        }
+        if pos == 2 {
+            equations.push(equation);
+            equation = ((0, 0, 0), (0, 0, 0));
+        }
+    }
+
+    equations
+}
+
+fn compute_price(equations: &Vec<((i64, i64, i64), (i64, i64, i64))>, offset: i64, allow_hundreds: bool) -> i64 {
+    let mut sum = 0;
+    for equation in equations {
+        let ((x1, x2, mut x_res), (y1, y2, mut y_res)) = equation;
+        x_res += offset;
+        y_res += offset;
+        let determinant = x1 * y2 - x2 * y1;
+        if determinant != 0 {
+            let x = (y2 * x_res - x2 * y_res) / determinant;
+            let x_remain = (y2 * x_res - x2 * y_res) % determinant;
+            let y = (x1 * y_res - y1 * x_res) / determinant;
+            let y_remain  = (x1 * y_res - y1 * x_res) % determinant;
+            if x_remain == 0 && (allow_hundreds || (0..=100).contains(&x) && y_remain == 0 && (0..=100).contains(&y)) {
+                sum += 3 * x + y;
+            }
+        }
+    }
+
+    sum
+}
+
+fn part_1(equations: &Vec<((i64, i64, i64), (i64, i64, i64))>) -> i64 {
+    compute_price(&equations, 0, false)
+}
+
+fn part_2(equations: &Vec<((i64, i64, i64), (i64, i64, i64))>) -> i64 {
+    compute_price(&equations, 10000000000000, true)
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let equations = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&equations));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&equations));
+    }
+}