#include <bits/stdc++.h>

#define pb push_back
#define f first
#define s second
#define pii pair<int, int>
#define mp make_pair

using namespace std;

const string name = "bmatrix",
             in_file = name + ".in",
             out_file = name + ".out";

ifstream fin(in_file);
ofstream fout(out_file);

const int MAX = 205;

int n, m;
int matrix[MAX][MAX];
int heights[MAX][MAX];
vector<int> stackk;
int lefty[MAX], righty[MAX];
int dp[MAX][MAX];

void build_heights(int line) {
    memset(heights, 0, sizeof(heights));

    for (int i = line + 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (matrix[i][j]) {
                heights[i][j] = 0;
            } else {
                heights[i][j] = heights[i - 1][j] + 1;
            }
        }
    }

    for (int i = 1; i <= line; i++) {
        for (int j = 1; j <= m; j++) {
            if (matrix[i][j]) {
                heights[i][j] = 0;
            } else {
                heights[i][j] = heights[i - 1][j] + 1;
            }
        }
    }
}

int go(int x1, int y1, int x2, int y2) {
    int maxx = 0;
    for (int i = x1; i <= x2; i++) {
        stackk.clear();
        stackk.push_back(0);
        heights[i][0] = -1;

        for (int j = y1; j <= y2; j++) {
            int height = heights[i][j];

            while (!stackk.empty() && heights[i][stackk.back()] >= height) {
                stackk.pop_back();
            }

            lefty[j] = stackk.back();
            stackk.push_back(j);
        }

        stackk.clear();
        stackk.push_back(m + 1);
        heights[i][m + 1] = -1;

        for (int j = y2; j > 0; j--) {
            int height = heights[i][j];

            while (!stackk.empty() && heights[i][stackk.back()] >= height) {
                stackk.pop_back();
            }

            righty[j] = stackk.back();
            stackk.push_back(j);
        }

    for (int j = y1; j <= y2; j++) {
        dp[i][j] = heights[i][j] * (righty[j] - lefty[j] - 1);
        maxx = max(dp[i][j], maxx);
    }
}
return maxx;
}

int main() {
    fin >> n >> m;

    string str;
    for (int i = 1; i <= n; i++) {
        fin >> str;
        for (int j = 1; j <= m; j++) {
            matrix[i][j] = str[j - 1] - '0';
        }
    }

    int result = 0;
    for (int line = 1; line < n; line++) {
        build_heights(line);
        int topLeftSecond = line + 1, bottomRightFirst = line;
        result = max(result, go(1, 1, bottomRightFirst, m) +
                     go (topLeftSecond, 1, n, m));
    }
    fout << result;
    return 0;
}