#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <fstream>


size_t maxZeroRectangle(size_t rows, size_t columns)
{

    std::string key;
    std::vector<std::vector<int>> field;

    std::getline(std::cin, key);
    for (size_t i = 0; rows > i; ++i)
    {
        std::getline(std::cin, key);
        std::vector<int> vector;

        vector.reserve(key.size());
        for (int j = 0; j < key.size(); ++j)
        {
            vector.push_back((key[j] - 47) % 2);
        }
        field.push_back(vector);
        vector.clear();


    }
    int result = -1;
    for (size_t i = 0; i < rows; ++i)
    {
        for (size_t j = 0; j < columns; ++j)
        {
            if (!field[i][j] || i == 0)
                continue;
            field[i][j] += field[i - 1][j];
        }


        int x = 0, y = 0, temp = 0;

        int m = *std::max_element(field[i].begin(), field[i].end());
        for (int j = 1; j <= m; ++j)
        {

            for (size_t k : field[i])
            {
                if (j > k)
                {
                    x = std::max(x, y);
                    y = 0;
                } else
                {
                    if (k == 0)
                    {
                        x = std::max(x, y);
                        y = 0;
                    } else
                        y++;
                }

            }
            x = std::max(x, y);
            temp = (int) (std::max(temp, j * x));
            x = 0;
            y = 0;
        }

        result = std::max(temp, result);
    }

    return result;
}


int main()
{
    size_t height, width;
    std::cin >> height >> width;


    std::cout << maxZeroRectangle(height, width);

    return 0;
}