Depth first search implementation

using System;
//Write a program that finds the largest area of equal neighbor elements in a rectangular matrix and prints its size
class Program
{
    static int[,] matrix = {
                           {1,3,2,2,2,4},
                           {3,3,3,2,4,4},
                           {1,3,1,2,3,3},
                           {4,3,1,3,3,1},
                           {4,3,3,3,1,1}, //not work for value 0 coz zero is used to mark
                           };
    static int model;
    static int score = 0;
    static int bestScore = 0;
    static int bestModel;


    static void Main()
    {
        for (int x = 0; x < matrix.GetLength(0); x++)
        {
            for (int y = 0; y < matrix.GetLength(1); y++)
            {
                model = matrix[x,y];
                score = 0;
                CheckPoint(x, y);
            }
        }
        Console.WriteLine(bestScore+" "+bestModel);
    }

    private static void CheckPoint(int x, int y)
    {
        //bottom of recursion
        if (x < 0 || x >= matrix.GetLength(0) || y < 0 || y >= matrix.GetLength(1))
        {
            return;
        }
        if (matrix[x,y] != model)
        {
            return;
        }
        //count score
        score++;
        if (score > bestScore)
        {
            bestScore = score;
            bestModel = model;
        }

        matrix[x, y] = 0; //mark as visited
        //call recursion for all directions
        CheckPoint(x, y+1); //rigth
        CheckPoint(x+1, y); //down
        CheckPoint(x, y-1); //left
        CheckPoint(x-1, y); // up
        matrix[x, y] = model; //unmark

    }
}