class Demo {
    static int fib(int n) {
	if (n <= 2)
		return 1;
	int result = 0;
	int fibnminus1 = 1;
	int fibnminus2 = 1;
	for (int i = 3; i <= n; i++) {
		result = fibnminus1 + fibnminus2;
		fibnminus2 = fibnminus1;
		fibnminus1 = result;
	}
	return result;
    }

    public static void main (String[] args) {
	int x = Integer.parseInt(args[0]);
	int xn = fib(x);
	System.out.println(xn);
    }
}