Override operators and to string

using System;
using System.Text;
//Write a class Matrix, to holds a matrix of integers. Overload the operators for adding, subtracting and multiplying
//of matrices, indexer for accessing the matrix content and ToString().
class Matrix
{
    public int rows;
    public int cols;
    private int[,] matrix;

    public Matrix(int x,int y)
    {
        matrix = new int[x, y];
        rows = x;
        cols = y;
    }

    public int this[int x, int y]
    {
        get
        {
            return matrix[x, y];
        }

        set
        {
            matrix[x, y] = value;
        }
    }

    public static Matrix operator +(Matrix matrix1, Matrix matrix2)
    {
        Matrix result = new Matrix(matrix1.rows, matrix1.cols);

        for (int x = 0; x < matrix1.rows ; x++)
        {
            for (int y = 0; y < matrix1.cols; y++)
            {
                result[x, y] = matrix1[x, y] + matrix2[x, y];
            }
        }
        return result;
    }

    public static Matrix operator -(Matrix matrix1, Matrix matrix2)
    {
        Matrix result = new Matrix(matrix1.rows, matrix1.cols);

        for (int x = 0; x < matrix1.rows; x++)
        {
            for (int y = 0; y < matrix1.cols; y++)
            {
                result[x, y] = matrix1[x, y] - matrix2[x, y];
            }
        }
        return result;
    }

    public static Matrix operator *(Matrix matrix1, Matrix matrix2)
    {
        Matrix result = new Matrix(matrix1.rows, matrix1.cols);

        for (int x = 0; x < matrix1.rows; x++)
        {
            for (int y = 0; y < matrix1.cols; y++)
            {
                result[x, y] = matrix1[x, y] * matrix2[y, x];
            }
        }
        return result;
    }

    public override string ToString()
    {
        StringBuilder result = new StringBuilder();
        for (int x = 0; x < this.rows; x++)
        {
            for (int y = 0 ;y  < this.cols;y ++)
            {
                if (y == 0)
                {
                    result.Append("\n{").Append(this[x, y]);
                }
                else
                {
                    result.Append(",").Append(this[x, y]);
                }
                if (y == this.cols - 1)
                {
                    result.Append("}");
                }
            }
        }
        return result.ToString();
    }

}

class Program
{

    static void Main()
    {

        Matrix m1 = new Matrix(5,5);
        Matrix m2 = new Matrix(5,5);
        Random generator = new Random();
        for (int x = 0; x < m1.rows; x++)
        {
            for (int y = 0; y < m1.cols; y++)
            {
                m1[x, y] = generator.Next(100);
                m2[x, y] = generator.Next(100);
            }
        }

        Console.Write("Adding:");
        Console.WriteLine((m1+m2).ToString());

        Console.Write("Subtracting:");
        Console.WriteLine((m1 - m2).ToString());

        Console.Write("Multiplying:");
        Console.WriteLine((m1 * m2).ToString());
    }
}