How to avoid NZEC error in C#?

[Begemot]

I try to solve BITMAP using C#, but i'm always get NZEC. This my code:

using System;
class Bitmap
{
    private static int[,] matrix;
    static void SetAround(int i, int j, int n, int m)
{
    if (i + 1 < n)
        if (matrix[i + 1, j] == -1)
            matrix[i + 1, j] = matrix[i, j] + 1;
    if (i - 1 >= 0)
        if (matrix[i - 1, j] == -1)
            matrix[i - 1, j] = matrix[i, j] + 1;
    if (j + 1 < m)
        if (matrix[i, j + 1] == -1)
            matrix[i, j + 1] = matrix[i, j] + 1;
    if (j - 1 >= 0)
        if (matrix[i, j - 1] == -1)
            matrix[i, j - 1] = matrix[i, j] + 1;
}

static void GetMin(int n, int m)
{
    bool isNull = true;
    while (isNull)
    {
        isNull = false;
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < m; j++)
            {
                if (matrix[i, j] == 0 | matrix[i, j] != -1)
                    SetAround(i, j, n, m);
                else
                    isNull = true;                    
            }
        }
    }
}

public static void Main()
{
    int k;
    int n;
    int m;
    string temp;

    k = Convert.ToInt32(Console.ReadLine());
    for (int i = 0; i < k; i++)
    {
        temp = Console.ReadLine();
        n = Convert.ToInt32(temp.Substring(0, temp.IndexOf(" ")));
        m = Convert.ToInt32(temp.Substring(temp.IndexOf(" "), temp.Length - temp.IndexOf(" ")));

        matrix = new int[n, m];

        // Read matrix and if 1 than put 0, and put -1 if 0;
        for (int j = 0; j < n; j++)
        {
            temp = Console.ReadLine();
            for (int l = 0; l < m; l++)
                if (Convert.ToInt32(temp[l]-'0') == 1)
                    matrix[j, l] = 0;
                else
                    matrix[j, l] = -1;
        }

        // Calculate min way to white for all matrix
        GetMin(n, m);

        // Print results
        for (int j = 0; j < n; j++)
        {
            for (int l = 0; l < m; l++)
                Console.Write(matrix[j, l] + " ");
            Console.WriteLine();
        }
    }
}
}

Thank you.