E04MaximalSum

public static void main(String[] args) throws IOException {
        BufferedReader rd = new BufferedReader(new InputStreamReader(System.in));

        int[][] matrix = readMatrix(rd);
        int[][] bestM = new int[3][3];
        int max = 0;

        for (int i = 0; i < matrix.length - 2; i++) {
            for (int j = 0; j < matrix[i].length - 2; j++) {

                int[][] mat = getNewMatrix(matrix, i, j);
                int sum = getSum(mat);

                if (sum > max) {
                    max = sum;
                    bestM = mat;
                }
            }
        }

        System.out.println("Sum = " + max);
        printMatrix(bestM);
    }

    private static int getSum(int[][] mat) {
        int sum = 0;
        for (int[] ints : mat)
            sum += Arrays.stream(ints).sum();
        return sum;
    }

    private static int[][] getNewMatrix(int[][] matrix, int i, int j) {
        int[][] mat = new int[3][3];
        for (int k = 0; k < 3; k++)
            mat[k] = Arrays.copyOfRange(matrix[i + k], j, j + 3);
        return mat;
    }

    private static void printMatrix(int[][] ar) {
        for (int[] nums : ar)
            System.out.println(Arrays.toString(nums).replaceAll("[\\[\\],]", ""));
    }

    private static int[][] readMatrix(BufferedReader rd) throws IOException {
        int[] size = Arrays.stream(rd.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
        int[][] mat = new int[size[0]][size[1]];
        for (int i = 0; i < mat.length; i++)
            mat[i] = Arrays.stream(rd.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
        return mat;
    }