#include <bits/stdc++.h>
using namespace std;
/// DREPTUNGHI DE ARIE MAXIMA SUB HISTOGRAMA
int MaxArea(int hist[], int n){
    stack<int> s;
    int Max=0,i=0;
    while(i<n){
        if(s.empty()||hist[s.top()]<=hist[i])
            s.push(i++);
        else{
            int top=s.top();
            s.pop();
            int Area;
            if(s.empty()) Area=hist[top]*i;
            else Area= hist[top]*(i-s.top()-1);
            if(Area>Max)
                Max=Area;
        }
    }
    while(!s.empty()){
        int top=s.top();
        s.pop();
        int Area;
        if(s.empty()) Area=hist[top]*i;
        else Area=hist[top]*(i-s.top()-1);
        if(Area>Max) Max=Area;
    }
    return Max;
}
int Largest(char A[205][205],int n,int m){
    int v[205]={0};
    int Max=-1;
    for(int i=1;i<=n;++i){
        for(int j=1;j<=m;++j)
            if(A[i][j]=='0') ++v[j-1];
            else v[j-1]=0;
        int Sol=MaxArea(v,m);
        if(Sol>Max)
            Max=Sol;
    }
    return Max;
}
char A[205][205],X[205][205],Y[205][205];
int main(){
    freopen("bmatrix.in","r",stdin);
    freopen("bmatrix.out","w",stdout);
    int n,m;
    scanf("%d %d\n",&n,&m);
    for(int i=1;i<=n;++i)
        fgets(A[i]+1,205,stdin);
    int Max=-1;
    /// CAZ 1 TAIETURA VERTICALA
    for(int k=0;k<=m;++k){
        for(int i=1;i<=n;++i)
            for(int j=1;j<=m;++j)
                if(j<=k) X[i][j]=A[i][j];
                else Y[i][j-k]=A[i][j];
        int Sol=Largest(X,n,k)+Largest(Y,n,m-k);
        if(Sol>Max)
            Max=Sol;
    }
    /// CAZ 2 TAIETURA ORIZONTALA
    for(int k=0;k<=n;++k){
        for(int i=1;i<=n;++i)
            for(int j=1;j<=m;++j)
                if(i<=k) X[i][j]=A[i][j];
                else Y[i-k][j]=A[i][j];
        int Sol=Largest(X,k,m)+Largest(Y,n-k,m);
        if(Sol>Max)
            Max=Sol;
    }
    printf("%d\n",Max);
    return 0;
}