using System;

public class Program
{
	public static void Main()
	{
		    Console.WriteLine("Enter in a number between 1-100.");
            int cMax = Convert.ToInt32(Console.ReadLine());

            int sum = 0;
            for(int i = 0; i <= cMax; i++)
			{
				sum += i;
			}

            Console.WriteLine(sum);
            Console.ReadLine();
	}
}