/**
 * Created by Casper on 08-12-2015.
 */
public class FibIter {

    private static long fib_iter(long a) {
        long r = 0;
        long minus_one = 1;
        long minus_two = 0;

        if (a == 0) {
            r = 0;
        } else if (a == 1) {
            r = 1;
        } else {
            for (long i = 2; i <= a; i++) {
                r = minus_one + minus_two;
                minus_two = minus_one;
                minus_one = r;
            }
        }
        return r;
    }


    public static void main(String[] args) {
        long a = 0;
        long r = 0;

        a = Long.parseUnsignedLong(args[0]);
        r = fib_iter(a);

        System.out.println("fib(" + Long.toUnsignedString(a) + ") = " + r);
    }
}