fn pow2(exponent: u32) -> u32 {
    var value: u32 = 1
    var i: u32 = 0
    while i < exponent {
        value = value * 2
        i = i + 1
    }
    return value
}

fn ackSmall(m: u32, n: u32) -> u32 {
    if m == 0 {
        return n + 1
    }
    if m == 1 {
        return n + 2
    }
    if m == 2 {
        return 2 * n + 3
    }
    if m == 3 {
        return pow2(n + 3) - 3
    }
    return 0
}

pub fn main(world: World) -> Void raises {
    if ackSmall(0, 4) == 5 && ackSmall(1, 4) == 6 && (ackSmall(2, 4) == 11 && ackSmall(3, 2) == 29) {
        check world.out.write("ackermann ok\n")
    }
}