#include <bits/stdc++.h>

using namespace std;

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

const int nmax = 205;

bool v[nmax][nmax];
int tmp[nmax][nmax];
int sum[nmax][nmax];
int st[nmax], dr[nmax];
int n, m;

int maxarea(vector<int> a)
{
    stack<pair<int, int>> s;

    for (int i = 0; i < a.size(); i++)
    {
        while (!s.empty() && s.top().first >= a[i])
        {
            s.pop();
        }
        int tmp = -1;
        if (!s.empty() && s.top().first < a[i])
            tmp = s.top().second;
        s.push({a[i], i});
        st[i] = tmp;
    }

    while (!s.empty())
        s.pop();

    for (int i = a.size() - 1; i >= 0; i--)
    {
        while (!s.empty() && s.top().first >= a[i])
        {
            s.pop();
        }
        int tmp = a.size();
        if (!s.empty() && s.top().first < a[i])
            tmp = s.top().second;
        s.push({a[i], i});
        dr[i] = tmp;
    }

    int res = 0;
    for (int i = 0; i < a.size(); i++)
    {
        res = max(res, (dr[i] - st[i] - 1) * a[i]);
    }

    return res;
}

int solve()
{
    memset(sum, 0, sizeof sum);

    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            sum[i][j] = (!v[i][j]) * sum[i - 1][j] + !v[i][j];
        }
    }

    int resa[nmax], resb[nmax];
    memset(resa, 0, sizeof resa);
    memset(resb, 0, sizeof resb);

    for (int i = 1; i <= n; i++)
    {
        vector<int> a, b;

        for (int j = 1; j <= m; j++)
            a.push_back(sum[i][j]);

        b.push_back(a.back());
        a.pop_back();

        while (!a.empty())
        {
            resa[a.size()] = max(maxarea(a), resa[a.size()]);
            resb[b.size()] = max(maxarea(b), resb[b.size()]);
            b.push_back(a.back());
            a.pop_back();
        }
    }
    int res = 0;

    for (int i = 1; i < m; i++)
    {
        res = max(res, resa[i] + resb[m - i]);
    }

    return res;
}

void rotate()
{

    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            tmp[i][j] = v[i][j];
        }
    }

    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            v[j][n - i + 1] = tmp[i][j];
        }
    }

    swap(n, m);
}

int main()
{
    in >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            char c;
            in >> c;
            v[i][j] = (c == '1');
        }
    }

    int res = solve();
    for (int i = 0; i < 3; i++)
    {
        rotate();
        res = max(res, solve());
    }
    out << res;
}