using System;

​

public class Program

{

    public static void Main()

    {

        int sum, flat,avg;

        Console.WriteLine("enter number of flats");

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

        sum = 0;

        avg=0;

        while (flat >= 0)

        {

            sum = sum + flat;

            avg++;

            Console.WriteLine("enter number of flats");

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

        }

​

        Console.WriteLine(sum + " flats were sold");

        Console.WriteLine("average=" +(sum/avg));

    }

}