#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>

using namespace std;
using ll = long long;
using namespace boost::multiprecision; 
using ull = cpp_int;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    ull N;
    cin >> N;
    cout << N*(N+1)/2 << endl;

    return 0;
}