#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

int main() {
    
    int sum = 0;
    int N;
    cin >> N;
    
    for ( int i = 1; i <= N; i++ ) {
        sum += i;
    }
    
    cout << sum << endl;
    return 0;
}