[C# Beginner Exam] Nine Digit Magic Numbers

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Nine_Digit_Magic_Numbers
{
    class MagicNumbers
    {
        static void Main(string[] args)
        {
            int sumOfNum = int.Parse(Console.ReadLine());
            int difference = int.Parse(Console.ReadLine());
            int counter = 0;

            for (int i1 = 1; i1 <= 7; i1++)
            {
                for (int i2 = 1; i2 <= 7; i2++)
                {
                    for (int i3 = 1; i3 <= 7; i3++)
                    {
                        for (int i4 = 1; i4 <= 7; i4++)
                        {
                            for (int i5 = 1; i5 <= 7; i5++)
                            {
                                for (int i6 = 1; i6 <= 7; i6++)
                                {
                                    int firstThree = int.Parse("" + i1 + i2 + i3);
                                    int secondThree = int.Parse("" + i4 + i5 + i6);

                                    if (secondThree - firstThree == difference && secondThree > firstThree)
                                    {
                                        for (int i7 = 1; i7 <= 7; i7++)
                                        {
                                            for (int i8 = 1; i8 <= 7; i8++)
                                            {
                                                for (int i9 = 1; i9 <= 7; i9++)
                                                {
                                                    if ((i1 + i2 + i3 + i4 + i5 + i6 + i7 + i8 + i9) == sumOfNum)
                                                    {
                                                        int lastThree = int.Parse("" + i7 + i8 + i9);

                                                        if (secondThree - firstThree == difference
                                                              && lastThree - secondThree == difference
                                                                  && lastThree > secondThree && secondThree > firstThree)
                                                        {
                                                            Console.WriteLine("" + i1 + i2 + i3 + i4 + i5 + i6 + i7 + i8 + i9);
                                                            counter++;
                                                        }
                                                    }
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }

            if (counter == 0)
            {
                Console.WriteLine("No");
            }

        }
    }
}