val int s 3; # global

val [int->int] fib (int n) {
    return if == n 0 {
        1
    } else {
        n * fib 
    };
};

val [->int] main {
    val str line input;
    val int n to_int line,;
    if < n 0 {
        print "illegal number"
    } else {
        print to_str fib n,;
    }
};