#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i <= (int)(n); i++)
typedef long long ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<vector<int>>> vvvi;
typedef vector<string> vs;
typedef vector<vector<string>> vvs;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
#define yes(ans) if(ans)cout << "yes"<< endl; else cout << "no" << endl
#define Yes(ans) if(ans)cout << "Yes"<< endl; else cout << "No" << endl
#define YES(ans) if(ans)cout << "YES"<< endl ;else cout << "NO" << endl

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