Solution Review: Find Two Numbers that Add Up to "Value"

using System;
using System.Collections.Generic;
namespace chapter_9
{  
    class challenge_10
    {
        static int[] findSum(int[] arr, int sum, int size)
        {
            HashSet<int> US = new HashSet<int>();
            int[] result = new int[2];
            for (int i = 0; i < size; i++)
            {
                int temp = sum - arr[i];
                US.Add(arr[i]);
                if (US.Contains(temp))
                {
                    result[0] = arr[i];
                    result[1] = temp;
                    return result;
                }
            }
            return arr;
        }
        static void Main(string[] args)
        {
            int size = 6, value = 8;
            int [] arr = { -1, -5, 45, 6, 10, 9 };
            if (size > 0)
            {
                int [] arr2 = findSum(arr, value, size);
                int num1 = arr2[0];
                int num2 = arr2[1];
                if ((num1 + num2) != value)
                    Console.WriteLine("Not Found");
                else
                {
                    Console.WriteLine("Number 1 = " + num1);
                    Console.WriteLine("Number 2 = " + num2);
                    Console.WriteLine ("Sum = " + (num1 + num2));
                }
            }
            else
            {
                Console.WriteLine("Input Array is Empty!");
            }
        }
    }
}