using System;

​

public class Grade

{

    public double total;

    public int n;

    public double g;

    public void input()

    {

        while (true)

        {

            Console.WriteLine("Grade?");

            g = Convert.ToInt32(Console.ReadLine());

            if(g == -1)

                break;

            else

            {

                total +=g;

                n++;

            }

        }

        Console.WriteLine("Total = " + total);

    }

​

    public void calculate() 

    {

        double avg = total/n;

        Console.WriteLine("Avg = {0}", avg);

    }

​

}

​

public class Factorial

{

    public int n;

    public double result = 1;

    public void calculate()

    {

        if(n<0)

            Console.WriteLine("Invalid input.");

        else if(n==0)

            Console.WriteLine("Factorial n = 1");

        else

        {

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

            {

                result = result*i;

            }

            Console.WriteLine("Factorial n = " + result);

        }

    }

}

​

public class Program

{

    public static void Main()

    {

/*

        Grade gr = new Grade();

        gr.input();

        gr.calculate();

*/

        Factorial f = new Factorial();      

        Console.WriteLine("Input n");

        f.n = Convert.ToInt32(Console.ReadLine());

        f.calculate();

    }

}

​