using System;
using System.Collections.Generic;
using System.IO;
class Solution
{
    static void Main(String[] args)
    {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution */
        int input = Console.Read();
        int total = 0;
        for (int i = 0; i <= input; i++)
        {
            total += i;
        }
        Console.Write(total);
    }
}