using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Nhap so n");

        int n;

        n = int.Parse(Console.ReadLine());

        int total = 0;

        for(int i = 1;i<=n;i++){

            total+=i;

        }

        Console.WriteLine("Result is " + total);

    }

}