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

using namespace std;

int N, M;
char A[202][202];
int up[202][202];
int lft[202], rgh[202];
int D[202], H[202];
int result;

int matrix(const int& i1, const int& j1, const int& i2, const int& j2)
{
	memset(up, 0, sizeof(up));
    for (int i = i1; i <= i2; ++i)
        for (int j = j1; j <= j2; ++j)
            if (A[i][j] == '0')
                up[i][j] = up[i - 1][j] + 1;
            else
				up[i][j] = 0;

    int resnow = 0;
    for (int i = i1; i <= i2; ++i)
    {
        D[0] = 0;
        for (int j = j1; j <= j2; ++j)
        {
            while (D[0] && up[i][j] <= up[i][D[D[0]]])
                --D[0];

            D[++D[0]] = j;
            H[D[D[0]]] = (D[0] != 1 ? D[D[0] - 1] + 1 : j1);

            lft[j] = j - H[D[D[0]]];
        }

        D[0] = 0;
        for (int j = j2; j >= j1; --j)
        {
            while (D[0] && up[i][j] <= up[i][D[D[0]]])
                --D[0];

            D[++D[0]] = j;
            H[D[D[0]]] = (D[0] != 1 ? D[D[0] - 1] - 1 : j2);

            rgh[j] = H[D[D[0]]] - j;
        }

        for (int j = j1; j <= j2; ++j)
            resnow = max(resnow, up[i][j] * (lft[j] + rgh[j] + 1));
    }

    return resnow;
}

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

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

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

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

    fout << result;

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