#include "bits/stdc++.h"
#define MAXN 100009
#define INF 1000000007
#define mp(x,y) make_pair(x,y)
#define all(v) v.begin(),v.end()
#define pb(x) push_back(x)
#define wr cout<<"----------------"<<endl;
#define ppb() pop_back()
#define tr(ii,c) for(__typeof((c).begin()) ii=(c).begin();ii!=(c).end();ii++)
#define ff first
#define ss second
#define my_little_dodge 46
#define debug(x) cerr<< #x <<" = "<< x<<endl;
using namespace std;
typedef long long ll;
typedef pair<int,int> PII;
template<class T>bool umin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool umax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
const int N=2509;
char arr[N][N];
int up[N][N],down[N][N],ans[N];
int main(){
int n,m;
scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
scanf(" %c",&arr[i][j]);
int h=n,w=m;
for(int i=1;i<=n;i++){
int cnt=0;
for(int j=1;j<=m;j++){
if(arr[i][j]=='1')
cnt++;
else{
if(cnt)
w=min(w,cnt);
cnt=0;
}
}
if(cnt)
w=min(w,cnt);
}
for(int j=1;j<=m;j++){
int cnt=0;
for(int i=1;i<=n;i++){
if(arr[i][j]=='1')
cnt++;
else{
if(cnt)
h=min(h,cnt);
cnt=0;
}
}
if(cnt)
h=min(h,cnt);
}
for(int j=1;j<=m;j++){
for(int i=1;i<=n;i++)
if(arr[i][j]=='1')
up[i][j]=up[i-1][j]+1;
for(int i=n;i>=1;i--)
if(arr[i][j]=='1')
down[i][j]=down[i+1][j]+1;
}
for(int i=1;i<=w;i++)
ans[i]=h;
for(int i=1;i<=n;i++){
int cnt=0,a=INF,b=INF;
for(int j=1;j<=m;j++){
if(arr[i][j]=='1'){
umin(a,up[i][j]);
umin(b,down[i][j]);
umin(ans[++cnt],a+b-1);
}
else
cnt=0,a=b=INF;
}
a=b=INF;cnt=0;
for(int j=m;j>=1;j--){
if(arr[i][j]=='1'){
umin(a,up[i][j]);
umin(b,down[i][j]);
umin(ans[++cnt],a+b-1);
}
else
cnt=0,a=b=INF;
}
}
int res=ans[1];
for(int i=2;i<=w;i++){
umax(res,i*ans[i]);
}printf("%d\n",res);
return 0;
}
