using System;

public class Program

{   static int TongSoNguyen(int n)

    {int s=0;

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

        {s=s+i;}

     return s;

    }

    public static void Main()

    {

        Console.WriteLine("Nhap N:");

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

        int s=0;

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

        {s=s+i;}

        Console.WriteLine("Tong cac so tu 1 den {0} la {1}",n,s);

        int t=TongSoNguyen(n);

        Console.WriteLine("Kiem tra lai voi ham ra ket qua {0}",t);

    }

}