#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
using namespace std;
#define rep(i, n) for(int i=0; i<(n); ++i)
#define FOR(i, m, n) for(int i=(m); i<(n); ++i)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define mp make_pair
#define pb push_back
#define Cout(x) cout << (x) << endl
#define Cout2(x, y) cout << (x) << " " << (y) << endl
#define dump(x) cout << #x << " = " << (x) << endl;
#define forauto(i, a) for(auto i : a)cout << i << " "; puts("");
typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<string> VS;
typedef vector<bool> VB;
typedef vector<vector<int>> VVI;
typedef pair<int, int> PII;
const int inf = 1e9;
const double pi = acos(-1.0);

int main() {
	VI num(10003);
	num[1] = 2;
	int x = 2;
	for (int i = 2; i <= 10000; i++) {
		num[i] = num[i - 1] + x;
		x++;
	}

	int n;
	while (cin >> n) {
		Cout(num[n]);
	}
}
