#include <iostream>
#include <string>
#include <stdlib.h>

using namespace std;

string s;

int main(void)
{
	cin >> s;
	
	if(s[0] > '0' && s[0] <= '9'){
		int n = atoi(s.c_str());
		cout << n*(n+1)/2 << endl;
		return 0;
	}
	
	cout << "Hello World!" << endl;
	return 0;
}