#include<iostream>
#include<algorithm>
#include<vector>
#include<cmath>
#include<string>
#include<numeric>
#include<algorithm>
using namespace std;
int main()
{
    vector <int> a;
    int n;
    cin >> n;
    for(int i=0;i<=n;i++)a.push_back(i);
    cout << accumulate(a.begin(),a.end(),0) <<endl;
}