#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cmath>
#include <vector>
#include <set>
#include <queue>
#include <unordered_map>
#include <map>
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
using lint = long long;
using namespace std;

const int MOD = 1000000007;

int main() {
    int N;
    cin >> N;
    cout << (N + 1) * N / 2 << endl;
    return 0;
}