A Simple program: Sum of Boundary elements of a Matrix

import java.util.*;
public class Boundary_Elements
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        int m, n, sum = 0, row1 = 0, col_n = 0, diag = 0;
        System.out.print("\nEnter the no. of rows : ");
        m = sc.nextInt();
        System.out.print("\nEnter the no. of columns : ");
        n = sc.nextInt();
        int i, j;
        int[][] mat = new int[m][n];
        System.out.print("\n Input "+ m*n +" matrix elements \n");
        for(i = 0; i < m; i++)
        {
            for(j = 0; j < n; j++)
            {
                  mat[i][j] = sc.nextInt();
            }
         }
     System.out.println("The original matrix is");
    for(i = 0; i < m; i++)
        {
            for(j = 0; j < n; j++)
            {
                 System.out.print(mat[i][j]+ " ");
                
            }
           System.out.println();
         }
        System.out.print("\n Boundary Matrix: \n");
        for(i = 0; i < m; i++)
        {
            for(j = 0; j < n; j++)
            {
                if (i == 0 || j == 0 || i == n-1|| j == n - 1)
                {
                   System.out.print(mat[i][j] + "  " );
                    sum = sum + mat[i][j];
                }
                else
                System.out.print("  ");
                
            }
            System.out.println( );
        }
        System.out.print("\n Sum of boundary elements is " + sum);
    }
}