#include <fstream>
#include <iostream>
std::ifstream fin("bmatrix.in");
std::ofstream fout("bmatrix.out");
char A[201][201];int S[201][201], dim1[201], dim2[201]; 
int main(){
    int n, m;
    fin >> n >> m;
    for(int i = 1; i <= n; i++){
        S[i][0] = 0;
        for(int j = 1; j <= m; j++){
            fin >> A[i][j];
            //S[i][j] = S[i][j - 1] + (A[i][j] - '0');
        }
    }
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            S[i][j] = S[i][j - 1] + (A[i][j] - '0');
        }
    }
    for(int left = 1; left <= m; left ++){
        for(int right = left; right <= m; right ++){
            int L = 1, R = 0, diffmx = 0;
            for(int i = 1; i <= n; i++){
                if(S[i][right] - S[i][left - 1] == 0){
                    R = i; 
                }
                else {
                    L = i + 1;
                    R = i;
                }
                if(diffmx < (R - L + 1))
                    diffmx = (R - L + 1);
                dim1[i] = std::max(dim1[i], diffmx * (right - left + 1));
            }
            //fout << diffmx << "\n";
        }
    }
    for(int left = 1; left <= m; left ++){
        for(int right = left; right <= m; right ++){
            int L = n + 1, R = n, diffmx = 0;
            for(int i = n; i >= 1; i--){
                if(S[i][right] - S[i][left - 1] == 0){
                    L = i; 
                }
                else {
                    R = i - 1;
                    L = i;
                }
                if(diffmx < (R - L + 1))
                    diffmx = (R - L + 1);
                dim2[i] = std::max(dim2[i], diffmx * (right - left + 1));
            }
        }
    }
    int sum_mx = 0;
    for(int i = 0; i <= n; i++){
        if(dim1[i] >= 0 && dim2[i] >= 0)
            sum_mx = std::max(dim1[i] + dim2[i + 1], sum_mx) ;
    }
    fout << sum_mx;
}