fn ladder(a: &[i64], b: &[i64]) -> Vec<i64> {
    let size = a.len();
    let mut r = vec![0i64; size];

    let max_b = *b.iter().max().unwrap();
    let mod_mask = (1i64 << max_b) - 1;

    let max_a = *a.iter().max().unwrap();
    let mut fib = vec![0i64, 1];
    for i in 2..(max_a as usize + 2) {
        fib.push((fib[i - 1] + fib[i - 2]) & mod_mask);
    }

    for i in 0..size {
        r[i] = fib[(a[i] + 1) as usize] & ((1i64 << b[i]) - 1);
    }

    r
}