#include<iostream>
#include<algorithm>
#include<cassert>
#include<vector>
#include<fstream>
#include<string>
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<queue>
#include<map>

using namespace std;
#define REP(i,m,n) for(long long i=m;i<n;++i)
#define INF 10000000000000000
#define MOD 1000000007
#define ll long long
#define mp make_pair
#define all(v) v.begin(),v.end()

int main() {
	int n;
	cin >> n;
	n = n*(n + 1) / 2;
	printf("%d\n", n);
	return 0;
}