#include <bits/stdc++.h>
using namespace std;
int N, M, up[202][202], lft[202], rgh[202], D[202], H[202], result;
char A[202][202];
ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");
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()
{
    fin >> N >> M;
    for(int i = 0; i < N; i++)
        fin >> A[i];
    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));
    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;
    return 0;
}