diff --git a/src/lib.rs b/src/lib.rs
index 2d5c05d..fa37bd6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -28,4 +28,5 @@ pub mod remove_duplicates_from_sorted_array;
 pub mod add_strings;
 pub mod flip_and_invert_image;
 pub mod leaf_similar;
-pub mod sum_of_left_leaves;
\ No newline at end of file
+pub mod sum_of_left_leaves;
+pub mod license_key_formatting;
\ No newline at end of file
diff --git a/src/license_key_formatting.rs b/src/license_key_formatting.rs
new file mode 100644
index 0000000..32559e6
--- /dev/null
+++ b/src/license_key_formatting.rs
@@ -0,0 +1,29 @@
+pub fn license_key_formatting(s: String, k: i32) -> String {
+    let s = s.to_uppercase().replace('-', "");
+    let mut result = String::new();
+    let mut cur = s.as_str();
+    while !cur.is_empty() {
+        let (chunk, rest) =
+            cur.split_at(std::cmp::max(0, cur.len() as isize - k as isize) as usize);
+        if result.is_empty() {
+            rest.clone_into(&mut result);
+        } else {
+            result = format!("{}-{}", rest, result);
+        }
+        cur = chunk;
+    }
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn example_1() {
+        assert_eq!(
+            license_key_formatting("5F3Z-2e-9-w".to_owned(), 4),
+            "5F3Z-2E9W"
+        );
+    }
+}