using System;
public class Program
{
    public static void Main()
    {
        int num = int.Parse(Console.ReadLine() ?? string.Empty);
        //string[] blockWidth = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');

        int result = 0;
        for (int i = 1; i <= num; i++)
        {
            result += i;
        }
        Console.WriteLine(result);
    }
}