#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <cfenv>
#include <cinttypes>
#include <cstdint>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <chrono>
#include <forward_list>
#include <initializer_list>
#include <random>
#include <ratio>
#include <regex>
#include <system_error>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <shared_mutex>
using namespace std;
using ll = long long;
//ライブラリを貼るところ




//ここまで



void solve(){
    unsigned long long N; cin >> N;
    cout << N * (N + 1) / 2 << "\n";
}



int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << setprecision(16) << fixed;

    int T = 1;
    for(int i = 0; i < T; ++i) solve();
}