Find the maximum sum of Hour glass in a matrix ?

import java.util.*;
public class Matrix
{
static void Hourglass(int r,int c,int a[][])
{
int max=a[0][0];
if(r<3 || c<3)
return;
for(int i=0;i<r-2;i++)
{
for(int j=0;j<c-2;j++)
{
int sum=0;
sum+=a[i][j]+a[i][j+1]+a[i][j+2]+a[i+1][j+1]+a[i+2][j]+a[i+2][j+1]+a[i+2][j+2];
if(sum>max)
max=sum;
}
}
System.out.print(max);
}
public static void main(String[] args)
{
Scanner s=new Scanner(System.in);
int r=s.nextInt();
int c=s.nextInt();
int a[][]=new int[r][c];
for(int i=0;i<r;i++)
for(int j=0;j<c;j++)
a[i][j]=s.nextInt();
Hourglass(r,c,a);
}
}