# include <iostream>
# include <cstring>
# include <cstdio>
# include <algorithm>
# include <cmath>
# include <iomanip>
using namespace std;
int main()
{
	int N, S = 0;
	cin >> N;
	for (int i = 1; i <= N; i++)
	{
		S = S + i;
	}
	cout << S << endl;
	return 0;
} 