#include <fstream>
#include <cstring>
#include <stack>
#define nmax 202
using namespace std;
ifstream cin("bmatrix.in");
ofstream cout("bmatrix.out");
int n,m,a[nmax][nmax],dp[nmax][nmax],sol;
string sir;
stack<int>s;
int solve(int ls,int cs,int lf,int cf){
    int ans=0;
    for(int i=ls;i<=lf;i++){
        for(int j=cs;j<=cf;j++){
            if(i==ls)
                dp[i][j]=1-a[i][j];
            else
                dp[i][j]=dp[i-1][j]+1-a[i][j];
            while(!s.empty()&&dp[i][s.top()]>dp[i][j]){
                ans=max(ans,dp[i][s.top()]*(j-s.top()));
                s.pop();
            }
            s.push(j);
        }
        while(!s.empty()){
            ans=max(ans,dp[i][s.top()]*(cf-s.top()+1));
            s.pop();
        }
    }
    return ans;
}
signed main()
{
    cin>>n>>m;
    for(int i=1;i<=n;i++){
        cin>>sir;
        for(int j=1;j<=m;j++)
            a[i][j]=sir[j-1]-'0';
    }
    /// impartim matricea in doua zone
    for(int i=1;i<n;i++)
        sol=max(sol,solve(1,1,i,m)+solve(i+1,1,n,m));
    for(int i=1;i<m;i++)
        sol=max(sol,solve(1,1,n,i)+solve(1,i+1,n,m));
    cout<<sol;
    return 0;
}