#include <bits/stdc++.h>
#define DIM 2502
using namespace std;
int n,m,i,j;
char s[DIM];
int dp_up[DIM][DIM],dp_down[DIM][DIM],dp_left[DIM][DIM],dp_right[DIM][DIM];
int a[DIM][DIM],dp[DIM];
int main (){
//ifstream cin ("bomb.in");
//ofstream cout ("bomb.out");
cin>>n>>m;
for (i=1;i<=n;i++){
cin>>s+1;
for (j=1;j<=m;j++)
a[i][j] = s[j] - '0';
}
for (i=1;i<=n;i++)
for (j=1;j<=m;j++){
if (a[i][j]){
dp_up[i][j] = 1 + dp_up[i-1][j];
dp_left[i][j] = 1 + dp_left[i][j-1];
}}
for (i=n;i;i--)
for (j=m;j;j--){
if (a[i][j]){
dp_down[i][j] = 1 + dp_down[i+1][j];
dp_right[i][j] = 1 + dp_right[i][j+1];
}}
/// pot sa am maxim dimensiunile h,w
/// dp[i] - latimea maxima a unui dreptunghi cu inaltimea i
for (i=1;i<=n;i++)
dp[i] = m+1;
int w = m, h = n;
for (i=1;i<=n;i++)
for (j=1;j<=m;j++){
if (!a[i][j])
continue;
w = min (w,dp_right[i][j] + dp_left[i][j] - 1);
h = min (h,dp_up[i][j] + dp_down[i][j] - 1);
dp[1] = min (dp[1],dp_left[i][j] + dp_right[i][j] - 1);
}
for (j=1;j<=m;j++){
int st = 0, dr = m+1, cnt = 0;
for (i=1;i<=n;i++){
if (a[i][j]){
st = max (st,j - dp_left[i][j] + 1);
dr = min (dr,j + dp_right[i][j] - 1);
cnt++;
dp[cnt] = min (dp[cnt],dr-st+1);
} else {
cnt = 0;
st = 0, dr = m+1;
}}}
/// trb sa fac acelasi lucru si invers
for (j=1;j<=m;j++){
int st = 0, dr = m+1, cnt = 0;
for (i=n;i;i--){
if (a[i][j]){
st = max (st,j - dp_left[i][j] + 1);
dr = min (dr,j + dp_right[i][j] - 1);
cnt++;
dp[cnt] = min (dp[cnt],dr-st+1);
} else {
cnt = 0;
st = 0, dr = m+1;
}}}
int sol = 0;
for (i=1;i<=h;i++){
if (i > 1)
dp[i] = min (dp[i],dp[i-1]);
sol = max (sol,dp[i] * i);
}
cout<<sol;
return 0;
}
