#include <bits/stdc++.h>
using namespace std;
using un=unsigned long long;

int main(){
    un n;
    cin >> n;
    if (n%2) {
        cout << n * ((n + 1) / 2) << endl;
    }
    else {
        cout << (n / 2) * (n + 1) << endl;
    }
}