#include <iostream>
#include <string>
using namespace std;

string S;

int main() {
	cin >> S;
	for (int i = 0; i < S.size(); i++) {
		if (S[i] >= 'a' && S[i] <= 'z') {
			cout << "Hello World!" << endl;
			return 0;
		}
	}
	int N = stoi(S);
	cout << N * (N + 1) / 2 << endl;
	return 0;
}