fn gcd(a: u32, b: u32) -> u32 {
    var left: u32 = a
    var right: u32 = b
    while right != 0 {
        let next: u32 = left % right
        left = right
        right = next
    }
    return left
}

pub fn main(world: World) -> Void raises {
    if gcd(84, 30) == 6 {
        check world.out.write("gcd ok\n")
    }
}