#include <iostream>
#include <utility>
#include <cstdio>
#include <queue>
#include <stack>
#include <algorithm>
#include <numeric>
#include <vector>
#include <set>
#include <map>
#include <string>
#include <cstring>
using namespace std;

#define ALL(a) (a).begin(), (a).end()

using ll = long long;
using P = pair<int, int>;

struct State {
    int v, cost;

    State(int v, int cost): v(v), cost(cost) {}

    // 昇順
    bool operator<(const State& s) const {
        return cost < s.cost;
    }
    // 降順
    bool operator>(const State& s) const {
        return cost > s.cost;
    }
};

void dump_vector(vector<int> vec) {
    for (int i = 0; i < vec.size(); i++) {
        cout << vec[i] << (i < vec.size() - 1 ? " " : "\n");
    }
}

int main() {
    int n;
    cin >> n;

    cout << n * (n + 1) / 2 << endl;
    return 0;
}