#define _USE_NATH_DEFINES
#include<cstdio>
#include <iostream>
#include<sstream>
#include<fstream>
#include<iomanip>
#include<algorithm>
#include<cmath>
#include<complex>
#include <string>
#include<vector>
#include<list>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<bitset>
#include<numeric>
#include<limits>
#include<climits>
#include<cfloat>
#include<functional>
#include<iterator>
#include <random>

using namespace std;
#define REP(i,m,n) for(int i=(int)m ; i < (int) n ; ++i )
#define rep(i,n) REP(i,0,n)
using ll = long long;
#define EPS 1e-9

int main() {
	int n;
	cin >> n;
	int ans = 0;
	REP(i, 1, n+1) {
		ans += i;
	}
	cout << ans << endl;
	return 0;
}