Maximal Sum From File

//Write a program that reads a text file containing a square matrix of numbers and finds in the matrix
//an area of size 2 x 2 with a maximal sum of its elements. The first line in the input file contains
//the size of matrix N. Each of the next N lines contain N numbers separated by space. The output
//should be a single number in a separate text file. Example:
//4
//2 3 3 4
//0 2 3 4       --->    17
//3 7 1 2
//4 3 3 2

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


class MaximalSumFromFile5
{


    private static int FindMaxSum(int[,] matrix)
    {

        int bestSum = int.MinValue;
        int currentSum = 0;

        for (int row = 0; row < matrix.GetLength(0) - 1; row++)
        {
            for (int col = 0; col < matrix.GetLength(1) - 1; col++)
            {
                currentSum = matrix[row, col] + matrix[row, col + 1] +
                             matrix[row + 1, col] + matrix[row + 1, col + 1];
                if (bestSum < currentSum)
                {
                    bestSum = currentSum;
                }
                currentSum = 0;
            }
        }
        return bestSum;
    }

    static void Main()
    {
        StreamReader read = new StreamReader("../../inputMatrix.txt");
        StreamWriter write = new StreamWriter("../../output.txt");
        string line = "";
        string number = "";
        int sizeOfMatrix;
        int row = 0;
        int col = 0;

        using (read)
        {
            // read size of matrix and make one with that size
            line = read.ReadLine();
            sizeOfMatrix = int.Parse(line);
            int[,] matrix = new int[sizeOfMatrix, sizeOfMatrix];

            while ((line = read.ReadLine()) != null)
            {
                // fills matrix with numbers
                foreach (var symbol in line)
                {
                    if (symbol != ' ')
                    {
                        number += symbol;
                    }
                    else
                    {
                        matrix[row, col] = int.Parse(number);
                        number = "";
                        col++;
                    }
                }
                matrix[row, col] = int.Parse(number);
                col = 0;
                row++;
                number = "";
            }

            // print in file the max sum
            using (write)
            {
                write.WriteLine(FindMaxSum(matrix));
            }
        }
    }
}