fn test_cross_assign_fixed_array() {
    number := 5
    ans := fib(number)

    println(ans)
    assert ans == 21
}

fn fib(n int) u64 {
    if n <= 0 {
        panic('Bad number')
    }
    return match n {
        1 | 2 {
            1
        }
        else {
            mut pair := [1, 2]!
            for _ in 0 .. n {
                pair[0], pair[1] = pair[1], pair[0] + pair[1]
            }
            pair[1]
        }
    }
}