Methods-Ex\Add and Subtract

using System;

namespace methods_exerci
{
    class Program
    {
        static void Main(string[] args)
        {
            int number = 0;
            Console.WriteLine(Sum(number));

        }

        static int Sum(int number)
        {
            int sum = 0;
            for (int i = 0; i < 3; i++)
            {
              number = int.Parse(Console.ReadLine());
                if(i < 2)
                {
                    sum += number;
                }
                else
                {
                    sum -= number;
                }

            }

            return sum;
        }
    }
}