fn main() {
    fn fib(n: i32) -> i32 {
        fn _fib(n: i32, a: i32, b: i32) -> i32 {
            match (n, a, b) {
                (0, _, _) => a,
                _         => _fib(n-1, a+b, a)
            }
        }

        _fib(n, 0, 1)
    }

    for n in 0..20 {
        println!("{}", fib(n));
    }
}