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Problem 1789 Matrix Swapping II

Accept: 39    Submit: 77
Time Limit: 5000 mSec    Memory Limit : 32768 KB

Problem Description

Given an N * M matrix with each entry equal to 0 or 1. We can find some rectangles in the matrix whose entries are all 1, and we define the maximum area of such rectangle as this matrix's goodness.

We can swap any two columns any times, and we are to make the goodness of the matrix as large as possible.

Input

There are several test cases in the input. The first line of each test case contains two integers N and M (1 ≤ N,M ≤ 1000). Then N lines follow, each contains M numbers (0 or 1), indicating the N * M matrix

Output

Output one line for each test case, indicating the maximum possible goodness.

Sample Input

1011 1001 0001 3 4 1010 1001 0001

Sample Output

2

Source

Multi-School Training Contest - TOJ Site #2

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