How to find Sum of digonal element and the element of the matrice and sum of diagonal element

package com.jav.two.d.array;

import java.util.Scanner;

public class Smallest_Element_Column {
	public static void main(String[] args) {
	Scanner sc=new Scanner(System.in);
	System.out.println("Enter The Row Size: ");
	int m=sc.nextInt();
	System.out.println("Enter The Column Size: ");
	int n=sc.nextInt();
	int a[][]=new int[m][n];
	for(int i=0;i<m;i++) {
		for(int j=0;j<n;j++) {
			a[i][j]=sc.nextInt();
		}
	}
	
	for(int i=0;i<m;i++) {
		for(int j=0;j<n;j++) {
			System.out.print(a[i][j]+" ");
		}
		System.out.println();
	}
	
int mul=1;
int sum=0;
for (int i=0;i<m;i++){
  for(int j=0;j<n;j++){
    if(i==j){
      sum=sum+a[i][j];
       mul=mul*a[i][j];
    System.out.println(a[i][j]);
    }
  }
}
System.out.println(mul);
System.out.println("SUM"+sum);
	}
}