check the maximum product in diagonal going through down - right
if ( ( i - 3 ) >= 0 && ( j - 3 ) >= 0 ) { result = arr [ i , j ] * arr [ i - 1 , j - 1 ] * arr [ i - 2 , j - 2 ] * arr [ i - 3 , j - 3 ] ; if ( max < result ) max = result ; }