#include <bits/stdc++.h>
using namespace std;

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

int n, m;
int h[205], stiva[205];
int sus[205], jos[205], st[205], soldr[205];
char s[205];
bool a[202][202];

int ariemax(int dim)
{
    int vf = 0, sol = 0;
    stiva[++vf] = 0;

    for (int i = 1; i <= dim + 1; i++)
    {
        while (vf != 0 && h[stiva[vf]] > h[i])
        {
            sol = max(sol, h[stiva[vf]] * (i - 1 - (stiva[vf - 1] + 1) + 1));
            --vf;
        }
        stiva[++vf] = i;
    }
    return sol;
}

int main() {
    fin >> n >> m;
    fin.get();

    for (int i = 1; i <= n; i++)
    {
        fin.getline(s, m + 2);
        for (int j = 1; j <= m; j++)
            a[i][j] = s[j - 1] - '0';
    }

    int sol = 0;

    //sus in jos
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
            if (a[i][j] == 0)
                h[j]++;
            else
                h[j] = 0;

        sus[i] = max(sus[i - 1], ariemax(m));
    }

    //jos in sus
    for (int j = 1; j <= m; j++)
        h[j] = !(a[n][j]);

    jos[n] = ariemax(m);

    for (int i = n - 1; i > 0; i--)
    {
        for (int j = 1; j <= m; j++)
            if (a[i][j] == 0)
                h[j]++;
            else
                h[j] = 0;

        jos[i] = max(jos[i + 1], ariemax(m));
    }

    //st spre dr
    for (int i = 1; i <= n; i++)
        h[i] = !(a[i][1]);

    st[1] = ariemax(n);

    for (int j = 2; j <= m; j++)
    {
        for (int i = 1; i <= n; i++)
            if (a[i][j] == 0)
                h[i]++;
            else
                h[i] = 0;

        st[j] = max(st[j - 1], ariemax(n));
    }

    //dr spre st
    for (int i = 1; i <= n; i++)
        h[i] = !(a[i][m]);

    soldr[m] = ariemax(n);

    for (int j = m - 1; j > 0; j--)
    {
        for (int i = 1; i <= n; i++)
            if (a[i][j] == 0)
                h[i]++;
            else
                h[i] = 0;

        soldr[j] = max(soldr[j + 1], ariemax(n));
    }
    for (int i = 1; i < n; i++)
        sol = max(sol, sus[i] + jos[i + 1]);

    for (int j = 1; j < m; j++)
        sol = max(sol, st[j] + soldr[j + 1]);

    fout << sol << '\n';
    return 0;
}