#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using llu = long long unsigned;

vector<ll> dx = { 0, 0, -1, 1};
vector<ll> dy = {-1, 1,  0, 0};

#define MOD 1000000007
int main() {
    int N;
    cin >> N;
    int result = 0;
    for (int i=1; i<=N; i++) {
        result += i;
    }
    cout << result << endl;
    return 0;
}