Strange matrix

using System;

namespace FillPrintMatrix
{
class Program
{
static void Main()
{
    Console.Write("Please enter the matix size: ");
    string input = Console.ReadLine();
    int N;
    int digit = 1;

    while (int.TryParse(input, out N) == false)
    {
        Console.Write("Please enter a valid integer!: ");
        input = Console.ReadLine();
    }
    int[,] Matrix = new int[N, N];
    Console.WriteLine();

    //// Variant A:
    for (int col = 0; col < N; col++)
    {
        for (int row = 0; row < N; row++)
        {
            Matrix[row, col] = digit;       //Fill in the matrix
            digit++;
        }
    }

    Console.WriteLine("This is variant A:");
    for (int row = 0; row < N; row++)
    {
        for (int col = 0; col < N; col++)
        {
            Console.Write("{0,4}", Matrix[row, col]);     //Print the matrix
        }
        Console.WriteLine();
    }
    digit = 1;
    Console.WriteLine();

    // Variant B:
    for (int col = 0; col < N; col++)
    {
        if(col % 2 == 0)
        {
            for (int row = 0; row < N; row++)
            {
                Matrix[row, col] = digit;       //Fill in the matrix
                digit++;
            }
        }
        else
        {
            for (int row = N-1; row >= 0; row--)
            {
                Matrix[row, col] = digit;       //Fill in the matrix
                digit++;
            }
        }
    }

    Console.WriteLine("This is variant B:");
    for (int row = 0; row < N; row++)
    {
        for (int col = 0; col < N; col++)
        {
            Console.Write("{0,4}", Matrix[row, col]);     //Print the matrix
        }
        Console.WriteLine();
    }
    digit = 1;
    Console.WriteLine();

    }
}
}
}