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