using System;
public class Program
{
    static void Main()
    {
        string s = Console.ReadLine();
        string[] t = s.Split(' ');
        int a = int.Parse(t[0]);
        int sum = 0;
        for(int i=1; i<a+1 ;i++){
        	sum = sum + i;
        }
        Console.WriteLine(sum );
    }
}