#include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "math.h"
#include "utility"
#include "map"

using namespace std;
const long long int MOD = 1000000007;

int N;

int main() {
	cin >> N;
	cout << (N*(N + 1)) / 2 << endl;;
	return 0;
}