#include <cstdio>
#include <iostream>
#include <queue>
#include <vector>
#include <fstream>
#include <algorithm>
#include <string>
#include <iomanip>
#include <cstring>
#include <map>
#include <iomanip>
#include <unordered_map>
#include <stack>
#include <bitset>
#define MOD 8192
#define pb push_back
#define INF 0x3f3f3f3f
#define ll long long
#define NMAX 205

using namespace std;

typedef pair<int, int> pii;

ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");

char v[NMAX][NMAX], aux[NMAX][NMAX];
int histograma[NMAX],stiva[NMAX],n,m;

int solve(int sus, int jos) {
    int i,j,area,maxarea=0,vf=0;

    for(i=1;i<=m+1;++i) histograma[i]=0;
    for(i=sus;i<=jos;++i) {
        vf=0;
        for(j=1;j<=m+1;++j) {
            if(v[i][j]=='1') histograma[j]=0;
            else ++histograma[j];

            if(j==m+1) histograma[j]=0;

            maxarea=max(maxarea,histograma[j]);
            while(vf>0 && histograma[stiva[vf]]>histograma[j]) {
                area=histograma[stiva[vf]]*(j-stiva[vf]);
                maxarea=max(maxarea,area);
                --vf;
            }

            stiva[++vf]=j;
        }
    }

    return maxarea;
}

int main() {
	int i,j,res=0;

	fin>>n>>m;
	for(i=1;i<=n;++i) fin>>(v[i]+1);

	for(i=1;i<n;++i)
		res=max(res,solve(1,i)+solve(i+1,n));

	swap(n, m);
    for(int i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            aux[i][j] = v[j][i];
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            v[i][j] = aux[i][j];

	for(i=1;i<n;++i)
		res=max(res,solve(1,i)+solve(i+1,n));

	fout<<res;

	return 0;
}