#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using ull = unsigned long long;

#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
using mint = modint998244353;

random_device rnd;
mt19937 mt(rnd());
int RandInt(int a, int b) {
    return a + mt() % (b - a + 1);
}

const int dx[4] = {0, 1, 0, -1};
const int dy[4] = {1, 0, -1, 0};

int main(){
    ull n;
    cin>>n;
    ull ans;
    if(n%2==1){
        ans=(1+n)/2*n;
    }else{
        ans=n/2*(1+n);
    }
    cout<<ans<<endl;
    return 0;
}