Sum of Boundary Elements

import java.util.*;
class SumBoundaryElements
{
    public static void main(String args[])
    {
        int sum=0;
        Scanner sc=new Scanner(System.in);
        int ar[][]=new int[4][4];
        System.out.println("Enter matrix elements:-");
        for(int i=0;i<4;i++)
        {
            for(int j=0;j<4;j++)
            {
                ar[i][j]=sc.nextInt();
            }
        }
        for(int i=0;i<4;i++)
        {
            for(int j=0;j<4;j++)
            {
                if(i==0||i==3||j==0||j==3)
                {
                    sum=sum+ar[i][j];
                }
            }
        }
        System.out.println("Sum of boundary elements: "+sum);
    }
}