Hayvan Numbers (100/100)

using System;
using System.Collections.Generic;
using System.Linq;

namespace HayvanNumbers
{
    class HayvanNumbers
    {
        static void Main()
        {
            int sum = int.Parse(Console.ReadLine());
            int diff = int.Parse(Console.ReadLine());
            int count = 0;
            for (int first = 555; first <= 999; first++)
            {
                int second = first + diff;
                int third = second + diff;
                List<int> individualSums = new List<int>();
                int[] firstSplit = Array.ConvertAll(first.ToString().ToArray(), x=>(int)x - 48);
                int[] secondSplit = Array.ConvertAll(second.ToString().ToArray(), x => (int)x - 48);
                int[] thirdSplit = Array.ConvertAll(third.ToString().ToArray(), x => (int)x - 48);
                if (firstSplit.Sum() + secondSplit.Sum() + thirdSplit.Sum() == sum && isValidNum(firstSplit)
                    && isValidNum(secondSplit) && isValidNum(thirdSplit))
                {
                    Console.Write("{0}{1}{2}",first,second,third);
                    Console.WriteLine();
                    count++;
                }
            }
            if (count==0)
            {
                Console.WriteLine("No");
            }
        }

        static bool isValidNum(params int[] values)
        {
            for (int i = 0; i < values.Length; i++)
            {
                if (values[i] < 5 || values[i] > 9)
                {
                    return false;
                }
            }
            return true;
        }
    }
}