#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll inf=144499999999994;
ll mod=1000000007;
int main(){
    ll n;
    cin >> n;
    cout << (n*(n+1))/2 << endl;
}