Solution

1. ```
   fn fib(n: u32) -> u32 {
   ```
2. ```
       if n < 2 {
   ```
3. ```
           return n;
   ```
4. ```
       } else {
   ```
5. ```
           return fib(n - 1) + fib(n - 2);
   ```
6. ```
       }
   ```
7. ```
   }
   ```

9. ```
   fn main() {
   ```
10. ```
        let n = 20;
    ```
11. ```
        println!("fib({n}) = {}", fib(n));
    ```
12. ```
    }
    ```