func collatz_num[n: I64] : I64
    if n % 2 == 0
        return n / 2
    return n * 3 + 1

func collatz_seq[n: I64]: I64
    let i: I64 = 1
    while n != 1
        n = collatz_num(n)
        i = i + 1
    return i

func main[] : I64
    let max: I64 = 0
    let max_index: I64 = 0

    for i in 1..1000000
        let seq: I64 = collatz_seq(i)
        if seq > max
            max = seq
            max_index = i
    io.println_i64(max_index)