using System;

​

public class Program

{

    public static void Main()

    {

        double sum = 0;

        for (int j=1; j<=3; j++)

            { Console.WriteLine("how many students in class course:");

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

         double paycheck = payment(num_student);

         sum = sum +paycheck;

            }

         double avg = sum/3;

         Console.WriteLine("avg: " + avg);

​

    }

    public static int payment(int students)

    { 

        int money =0;

    if(students<=10)

        { money = money + 180;

        }

         else

        {

            money = 180; 

            for (int i = 11; i <= students; i++)

            {

                money = money + 5; 

            }

        }

         return money;

​

    }

}