#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <cmath>
#include <cctype>
#include <ctime>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define eps 1e-9

typedef long long ll;
typedef pair<int, int> pii;

const int INF = 0x7fffffff;
int n, ans;

int main() {
#ifdef __AiR_H
    freopen("A.in", "r", stdin);
//    freopen("out.txt", "w", stdout);
#endif // __AiR_H
    scanf("%d", &n);
    ans = n * (n + 1) / 2;
    printf("%d\n", ans);
#ifdef __AiR_H
    printf("Time used = %.2fs\n", (double)clock() / CLOCKS_PER_SEC);
#endif // __AiR_H
    return 0;
}
