#include <cstring>
#include <fstream>
#include <algorithm>
#include <deque>

int N, M;
char A[202][202];
int up[202][202], result;
int left[202], right[202];
std::deque<int> D;

int matrix(int i1, int j1, int i2, int j2)
{
    for (int i = i1; i <= i2; ++i)
        for (int j = j1; j <= j2; ++j)
            if (A[i][j] == '0')
                up[i][j] = (i > i1 ? up[i - 1][j] + 1 : 1);

    int resnow = 0;
    for (int i = i1; i <= i2; ++i)
    {
        D.clear();

        for (int j = j1; j <= j2; ++j)
        {
            while (!D.empty() && up[i][j] < up[i][D.back()])
                D.pop_back();

            if (D.empty() || up[i][j] != up[i][D.back()])
                D.push_back(j);

            left[j] = j - D.back();
        }

        D.clear();

        for (int j = j2; j >= j1; --j)
        {
            while (!D.empty() && up[i][j] < up[i][D.back()])
                D.pop_back();

            if (D.empty() || up[i][j] != up[i][D.back()])
                D.push_back(j);

            right[j] = D.back() - j;
        }

        for (int j = j1; j <= j2; ++j)
            resnow = std::max(resnow, up[i][j] * (left[j] + right[j] + 1));
    }

    return resnow;
}

int main()
{
    std::ifstream fin("bmatrix.in");
    std::ofstream fout("bmatrix.out");

    fin >> N >> M;
    for (int i = 0; i < N; ++i)
        fin >> A[i];

    // for rows
    for (int i = 0; i < N - 1; ++i)
        result = std::max(result, matrix(0, 0, i, M - 1) + matrix(i + 1, 0, N - 1, M - 1));

    // for columns
    for (int i = 0; i < M - 1; ++i)
        result = std::max(result, matrix(0, 0, N - 1, i) + matrix(0, i + 1, N - 1, M - 1));

    fout << result;

    fin.close();
    fout.close();
}