class Main {
   void main() {
		int a;
		a = fib(20);
		write(a);
		writeln();
	}
	
	int fib(int n) {
 
      int fib;
      int fib2;

      if (n <= 1) {
         fib = n;
		} else { 
         fib  = fib(n-1);
         fib2 = fib(n-2);
		 	fib = fib + fib2;
		}   
		return fib;
    }
}