#include <fstream>
#include <cstring>
#define DIM 205

using namespace std;

ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");
int N,M,a[DIM][DIM],sol,sus[DIM],jos[DIM];
char s[DIM][DIM];
void rotate(){
    char b[DIM][DIM];
    for(int i=1;i<=N;i++)
        for(int j=1;j<=M;j++)
            b[M-j+1][i]=s[i][j];
    memcpy(s,b,sizeof(b));
    swap(N,M);
}
void solve(){
    int nr;
    for(int i=1;i<=N;i++){
        for(int j=1;j<=M;j++)
            if(s[i][j]=='0')
                a[i][j]=a[i-1][j]+1;
            else
                a[i][j]=0;
        sus[i]=jos[i]=0;
    }
    for(int i=1;i<N;i++)
        for(int j=i;j<=N;j++){
                nr=0;
            for(int k=1;k<=M;k++){
                if(a[j][k]>=j-i+1)
                    nr++;
                else
                    nr=0;
                sus[j]=max(sus[j],nr*(j-i+1));
                jos[i]=max(jos[i],nr*(j-i+1));
            }
        }
    for(int i=2;i<=N;i++)
        sus[i]=max(sus[i-1],sus[i]);
    for(int i=N-1;i>=1;i--)
        jos[i]=max(jos[i+1],jos[i]);
    for(int i=1;i<N;i++)
        sol=max(sol,sus[i]+jos[i+1]);
}
int main(){
    fin>>N>>M;
    for(int i=1;i<=N;i++)
        fin>>s[i]+1;
    solve();
    rotate();
    solve();
    fout<<sol;
    fin.close();fout.close();
    return 0;
}