#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int,int>;
#define rep2(i,a,n) for(int i = (a);i < (n);i++)
#define rep(i,n) rep2(i,0,n)
#define INF (1LL << 60)

int main(void){
    int n,sum = 0;
    cin >> n;
    
    for(int i = 1;i <= n;i++)sum += i;
    cout << sum << endl;
}