fn fibWordLen(n: u32) -> u32 {
    var a: u32 = 1
    var b: u32 = 1
    var i: u32 = 0
    while i < n {
        let next: u32 = a + b
        a = b
        b = next
        i = i + 1
    }
    return a
}

pub fn main(world: World) -> Void raises {
    if fibWordLen(6) == 13 {
        check world.out.write("fibonacci word ok\n")
    }
}