using System;

public class Program

{

    public static void Main()

    {

        static int Tinhtongtich(int n)

        {

            int T = 1;

            int S = 0;

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

            {

                T = T * i;

                S = S + T;

            }

            return S;

​

        }

        static void Main(string[] args)

        {

            Console.WriteLine("Nhap n:");

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

            int S = Tinhtongtich(n);

            Console.WriteLine(S);

        }

    }

}