#include <bits/stdc++.h>

#define NMAX 205

using namespace std;

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

char a[NMAX][NMAX], aux[NMAX][NMAX];
int N, M, limit, sol;

void rotateMatrix() {
    for (int i = 1; i <= N; ++i) {
        for (int j = 1; j <= M; ++j) {
            aux[i][j] = a[j][i];
        }
    }

    for (int i = 1; i <= N; ++i) {
        for (int j = 1; j <= M; ++j) {
            a[i][j] = aux[i][j];
        }
    }
}

int getMaxArea(int start, int stop) {
    vector < int > st;
    int zeros[NMAX], area = 0;
    memset(zeros, 0, sizeof(zeros));

    for (int i = start; i <= stop; ++i) {
        st.clear();
        for (int j = 1; j <= M + 1; ++j) {
            if (a[i][j] == '0') {
                ++zeros[j];
            } else {
                zeros[j] = 0;
            }

            if (j == M + 1) {
                zeros[j] = 0;
            }


            int top = 0;
            if (st.size()) {
                top = st.back();
            }

            while (st.size() && zeros[st.back()] > zeros[j]) {
                area = max(area, zeros[st.back()] * (top - st[st.size() - 2]));
                st.pop_back();
            }

            st.push_back(j);
        }
    }

    return area;
}

int main() {
    f >> N >> M;
    for (int i = 1; i <= N; ++i) {
        f >> (a[i] + 1);
    }

    limit = N >> 1;
    for (int i = 1; i <= limit; ++i) {
        sol = max(sol, getMaxArea(1, i) + getMaxArea(i + 1, N));
    }

    swap(N, M);
    rotateMatrix();
    limit = N >> 1;
    for (int i = 1; i <= limit; ++i) {
        sol = max(sol, getMaxArea(1, i) + getMaxArea(i + 1, N));
    }

    g << sol << '\n';
    return 0;
}