#include <bits/stdc++.h>

using namespace std;

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

int n, m, a[205], b[205], aux[205][205], maxim, st[205], dr[205];
char matrix[205][205];
stack <int> stiva;

int HistogramArea(int *v)
{
    while (stiva.size() > 0) stiva.pop();
    for (int i = 1; i <= m; ++i)
    {
        while (stiva.size() > 0 && v[i] <= v[stiva.top()]) stiva.pop();
        if (stiva.size() == 0) st[i] = 1;
        else st[i] = stiva.top() + 1;
        stiva.push(i);
    }
    while (stiva.size() > 0) stiva.pop();
    for (int i = m; i >= 1; --i)
    {
        while (stiva.size() > 0 && v[i] <= v[stiva.top()]) stiva.pop();
        if (stiva.size() == 0) dr[i] = m;
        else dr[i] = stiva.top() - 1;
        stiva.push(i);
    }
    int maxx = 0;
    for (int i = 1; i <= m; ++i)
        maxx = max(maxx, (dr[i] - st[i] + 1) * v[i]);
    return maxx;
}

void solve()
{
    for (int i = 1; i <= max(n, m); ++i)
        a[i] = b[i] = 0;
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            if (matrix[i][j] == '0')
                aux[i][j] = 1 + aux[i - 1][j];
        }
        a[i] = max(HistogramArea(aux[i]), a[i - 1]);
    }
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j) aux[i][j] = 0;
    for (int i = n; i >= 1; --i)
    {
        for (int j = 1; j <= m; ++j)
        {
            if (matrix[i][j] == '0')
                aux[i][j] = 1 + aux[i + 1][j];
        }
        b[i] = max(HistogramArea(aux[i]), b[i + 1]);
    }
    for (int i = 1; i < n; ++i)
    {
        maxim = max(maxim, a[i] + b[i + 1]);
    }
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j) aux[i][j] = 0;
}

void Rotate()
{
    char help[205][205];
    for (int j = 1; j <= m; ++j)
    {
        for (int i = 1; i <= n; ++i)
        {
            help[j][i] = matrix[i][j];
        }
    }
    swap(n, m);
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            matrix[i][j] = help[i][j];
        }
    }
}

int main()
{
    fin >> n >> m;
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
            fin >> matrix[i][j];
    solve();
    Rotate();
    solve();
    fout << maxim;
    fin.close();
    fout.close();
    return 0;
}