average of first n natural numbers and assign it to output1.If list contain any negative number, assign -1 to output1.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace sample

{

    class avg

    {

        public static void Main(string[] args)

        {

            avg a1 = new avg();

            int output = a1.avg1(7);

            Console.WriteLine("output is:{0}", output);

            Console.ReadLine();

        }

        int avg1(int x)

        {

            int sum = 0;

            if (x < 0)

            {

                return -1;

            }

            else

            {

                for (int i = 0; i <= x; i++)

                {

                    sum = sum + i;

                }

                return sum / x;

            }

        }

    }

}