C++ Problem about a Matrix

Please explain every step, and your method.

DESCRIPTION

Input a n*m matrix containing only 0 and 1 values.
Objective: Find its biggest submatrix, for which all the values are 0 s

INPUT

first line is two numbers n,m(n,m<=300) .
then n lines，each line has m digits，each digit is 0 or 1 .
Each digit is separated by one blank space.

OUTPUT

One number ，which represent the number of zeros inside that submatrix

SAMPLE INPUT


6 5
0 0 0 0 0
0 1 1 1 0
0 1 0 1 0
0 1 1 1 0
0 0 0 0 0
0 0 0 0 0

SAMPLE OUTPUT

10

HINT

This question ia relatively easy, there are many methods, for example you coud search for all the submatrix and check for each if it contains all zero values