using System;
class MainClass
{
	public static void Main(string[] args)
	{
	    string stdin = Console.ReadLine();
		long N = long.Parse(stdin);
		long x = 0;
		long sum = 0;
		
		for(long i = 1; i <= N; i++){
		    sum += i;
		}
		
		Console.WriteLine(sum);
	}
}