/*

This Submission is to determine how many 120/240 min const. delivery point there are.

//info
120 req. steps <= 5
*/
#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include<map>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <cassert>
#include<fstream>
#include <unordered_map>
#include <cstdlib>
#include <complex>
#include <cctype>
#include <bitset>
using namespace std;
typedef string::const_iterator State;
#define Ma_PI 3.141592653589793
#define eps 1e-5
#define LONG_INF 1e18
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007LL
#define MOD 998244353LL
#define seg_size 262144
#define REP(a,b) for(long long a = 0;a < b;++a)

unsigned long xor128() {
	static unsigned long x = time(NULL), y = 362436069, z = 521288629, w = 88675123;
	unsigned long t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
double dot(complex<double> a, complex<double> b) {
	return a.real() * b.real() + a.imag() * b.imag();
}
double gyaku_dot(complex<double> a, complex<double> b) {
	return a.real() * b.imag() - a.imag() * b.real();
}
double leng(complex<double> a) {
	return sqrt(a.real() * a.real() + a.imag() * a.imag());
}
double angles(complex<double> a, complex<double> b) {
	double cosine = dot(a, b) / (leng(a) * leng(b));
	double sine = gyaku_dot(a, b) / (leng(a) * leng(b));
	double kaku = acos(min((double)1.0, max((double)-1.0, cosine)));
	if (sine <= 0) {
		kaku = 2 * Ma_PI - kaku;
	}
	return kaku;
}
vector<int> convex_hull(vector<complex<double>> a) {
	vector<int> ans;
	double now_minnest = a[0].real();
	int now_itr = 0;
	REP(i, a.size()) {
		if (now_minnest > a[i].real()) {
			now_minnest = a[i].real();
			now_itr = i;
		}
	}
	ans.push_back(now_itr);
	complex<double> ba(0, 1);
	while (true) {
		int now_go = 0;
		double now_min = 0;
		double now_length = 0;
		int starter = ans[ans.size() - 1];
		for (int i = 0; i < a.size(); ++i) {
			if (i != starter) {
				double goa = angles(ba, a[i] - a[starter]);
				if (goa - now_min >= eps || (abs(goa - now_min) <= eps && (abs(a[i] - a[starter]) - now_length) >= eps)) {
					now_min = goa;
					now_go = i;
					now_length = abs(a[i] - a[starter]);
				}
			}
		}
		if (now_go == ans[0]) break;
		ans.push_back(now_go);
		ba = complex<double>(a[now_go] - a[starter]);
	}
	return ans;
}
int dp[2001][2001] = {};
int second_dp[2001][2001] = {};
int main() {
	iostream::sync_with_stdio(false);
	cin.tie(0);
	int h, w;
	cin >> h >> w;
	vector<vector<int>> go;
	/*
	REP(i, h) {
		string s;
		cin >> s;
		vector<int> A;
		REP(q, s.length()) {
			if (s[q] == '.')A.push_back(0);
			else A.push_back(1);
		}
		go.push_back(A);
	}
	*/
	int ans = 0;
	REP(t, 1) {
		/*
		REP(i, h) {
			for (int q = 0; q < w-1; ++q) {
				dp[i][q] = go[i][q] ^ go[i][q+1] ^ t;
			}
		}
		*/
		REP(i, h) {
			REP(q, w) {
				cin >> dp[i][q];
				dp[i][q] = (dp[i][q] + 1) % 2;
			}
		}
		for (int i = 0; i < h; ++i) {
			for (int q = w - 1; q >= 0; --q) {
				second_dp[i][q] = second_dp[i][q + 1] + 1;
				if (dp[i][q] == 0) {
					second_dp[i][q] = 0;
				}
			}
		}
		for (int i = 0; i < w; ++i) {
			stack<pair<int, int>> geko;
			for (int q = 0; q < h + 1; ++q) {
				if (geko.empty()) {
					geko.push(make_pair(second_dp[q][i], q));
				}
				else {
					if (geko.top().first < second_dp[q][i]) {
						geko.push(make_pair(second_dp[q][i], q));
					}
					else if (geko.top().first > second_dp[q][i]) {
						int genya = -1;
						while (geko.empty() == false && geko.top().first >= second_dp[q][i]) {
							pair<int, int> now = geko.top();
							geko.pop();
							ans = max(ans, (now.first) * (q - now.second));
							genya = now.second;
						}
						if (geko.empty() == true || geko.top().first != second_dp[q][i]) {
							geko.push(make_pair(second_dp[q][i], genya));
						}
					}
				}
			}
		}
	}
	cout << ans << endl;
}


Measured memory_bytes: 25056