#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
typedef pair<P,ll> Pll;
typedef pair<P,P> PP;
#define rep(i,a,n) for(int i = a;i < n;i++)
#define LINF (ll)1e17
#define INF 1e9
#define MOD 1e9+7
#define sMOD 1e5
#define fs first
#define sc second

ll gcd(ll a,ll b){
	if(!b) return a;
	return gcd(b,a%b);
}


signed main(){
	
	int n;
	cin >> n;
	cout << n*(n+1)/2 << endl;
	return 0;

}