Given a matrix (H × W) which contains only 1 and 0, find the area of the largest rectangle which only contains 0s.

Constraints

* 1 ≤ H, W ≤ 1,400

Input


H W
c1,1 c1,2 ... c1,W
c2,1 c2,2 ... c2,W
:
cH,1 cH,2 ... cH,W


In the first line, two integers H and W separated by a space character are given. In the following H lines, ci,j, elements of the H × W matrix, are given.

Output

Print the area (the number of 0s) of the largest rectangle.

Example

Input

4 5
0 0 1 0 0
1 0 0 0 0
0 0 0 1 0
0 0 0 1 0


Output

6
#include <stdio.h>
#include <iostream>
#include <stack>
#include <algorithm>
using namespace std;

#define MAX 1400

struct Rectangle
{
  int height;
  int pos;
};

int getLargestRectangle(int size, int buffer[])
{
  stack<Rectangle> S;
  int maxv = 0;
  buffer[size] = 0;

  for (int i = 0; i <= size; i++)
  {
    Rectangle rect;
    rect.height = buffer[i];
    rect.pos = i;
    if (S.empty())
    {
      S.push(rect);
    }
    else
    {
      if (S.top().height < rect.height)
      {
        S.push(rect);
      }
      else if (S.top().height > rect.height)
      {
        int target = i;
        while (!S.empty() && S.top().height >= rect.height)
        {
          Rectangle pre = S.top();
          S.pop();
          int area = pre.height * (i - pre.pos);
          maxv = max(maxv, area);
          target = pre.pos;
        }
        rect.pos = target;
        S.push(rect);
      }
    }
  }
  return maxv;
}

int H, W;
int buffer[MAX][MAX];
int T[MAX][MAX];

int getLargestRectangle()
{
  for (int j = 0; j < W; j++)
  {
    for (int i = 0; i < H; i++)
    {
      if (buffer[i][j])
      {
        // 汚れタイル
        T[i][j] = 0;
      }
      else
      {
        // 上から1,2,3と増える
        T[i][j] = (i > 0) ? T[i - 1][j] + 1 : 1;
      }
    }
  }

  int maxv = 0;
  for (int i = 0; i < H; i++)
  {
    maxv = max(maxv, getLargestRectangle(W, T[i]));
  }

  return maxv;
}

int main()
{
  scanf("%d %d", &H, &W);
  for (int i = 0; i < H; i++)
  {
    for (int j = 0; j < W; j++)
    {
      scanf("%d", &buffer[i][j]);
    }
  }

  cout << getLargestRectangle() << endl;

  return 0;
}
