// using what_next_day;

using System;

​

​

namespace my_app

{

    class Program

    {

        static void Main(string[] args)

        {

            // WhatNextDay.run();

            Console.WriteLine("N: ");

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

​

            int i = 1;

            int pre = 1;

            int result = 0;

            while (i <= n)

            {

                pre *= i;

                result += pre;

                i++;

            }

​

            Console.WriteLine($"Ket qua la {result}");

        }

    }

}

​