диагонал на матрица-метод за намиране на сумата

package com.company;


import java.io.IOException;


import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.util.*;
import java.util.stream.Collectors;

public class Main {


    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int size = Integer.parseInt(scanner.nextLine());
        int[][] matrix = new int[size][size];

        for (int r = 0; r < size; r++) {
            for (int c = 0; c < size; c++) {
                matrix[r][c] = scanner.nextInt();
            }
        }

        //  PrintMatrix(matrix);
        int mainDiagonal = getMainDiagonalSum(matrix);
        System.out.println(mainDiagonal);
    }

    private static int getMainDiagonalSum(int[][] matrix) {
        int sum = 0;
        int r = 0, c = 0;
        while (r < matrix.length && c < matrix[r].length) {
            sum += matrix[r][c];
            r++;
            c++;
        }


        return sum;
    }

    private static void PrintMatrix(int[][] matrix) {
        for (int r = 0; r < matrix.length; r++) {
            for (int c = 0; c < matrix[r].length; c++) {
                System.out.print(matrix[r][c] + " ");
            }
            System.out.println();
        }
    }


}