using System;

public class Program

{//Bài 11: Tính S(n) = 1 + 1.2 + 1.2.3 + … + 1.2.3….N

    public static int Giaithua(int n)

    {   int T= 1;

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

        { T = T *i;}

        return T;

    }

    public static void Main()

    {   int S = 0;

        Console.WriteLine("nhap N: ");

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

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

        { S = S + Giaithua(i);}

        Console.WriteLine(S);

    }

}