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 <iostream>
#include <sstream>
#include <regex>
#include <cstdio>
#include <cmath>
#include <cctype>
#include <string>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>
#include <functional>
#include <iomanip>
#include  <cassert>
#include <fstream>
#include <codecvt>

using namespace std;
using ll = long long int;
#define rep(i,n) for(int i = 0; i < n; i++)
#define FOR(i, a, b)  for(int i = (a); i < (b) ; i++)
#define pb push_back
#define SORT(v,n) sort(v, v+n)
#define ALL(x) (x).begin(),(x).end()
#define debug(x) cerr << #x << ": " << x << '\n'
#define elif else if
#define int ll
const int INF = (1LL << 32);
const int MOD = (int)1e9 + 7;
const double EPS = 1e-9;
int dx[8] = { 1, 0, -1, 0, 1, -1, -1, 1 };
int dy[8] = { 0, 1, 0, -1, 1, 1, -1, -1 };

static const int 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() and S.top().height >= rect.height) {
					Rectangle pre = S.top();
					S.pop();
					int area = pre.height * (i - pre.pos);
					maxv = max(area, maxv);
					target = pre.pos;
				}
				rect.pos = target;
				S.push(rect);
			}
		}
	}
	return maxv;
}

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

int getLargestRectangle() {
	rep(j, W) {
		rep(i, H) {
			if (buffer[i][j]) {
				T[i][j] = 0;
			}
			else {
				T[i][j] = (i > 0) ? T[i - 1][j] + 1 : 1;
			}
		}
	}

	int maxv = 0;
	rep(i, H) {
		maxv = max(maxv, getLargestRectangle(W, T[i]));
	}
	return maxv;
}

signed main() {
	ios::sync_with_stdio(true);
	cin >> H >> W;
	rep(i, H) {
		rep(j, W) {
			cin >> buffer[i][j];
		}
	}
	cout << getLargestRectangle() << endl;
	return 0;
}
