#include <iostream>
using namespace std;

int main()
{
    int sum = 0;
    int N = 0;
    
    do
    {
        cin >> N;
    } while (N < 1 || N > 100);
    
    int i;
    for (i = 1; i <= N; i++)
    {
        sum += i;
    }
    
    cout << sum << endl;
    return 0;
}