#include <bits/stdc++.h>
using namespace std;

void solve1() {
    cout << "Hello World!" << endl;
}

bool solved2;
void solve2(stringstream& ss) {
    if (solved2) {

    } else {
        int n;
        ss >> n;
        cout << n * (n + 1) / 2 << endl;
    }
}

int main() {
    stringstream ss;
    char c;
    while ((c = getchar()) != EOF) {
        ss << c;
    }
    if (ss.str().size() == 0) {
        solve1();
    } else if (ss.str().size() < 4) {
        solve2(ss);
    }
}