/******************************************************************************
Welcome to GDB Online.
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C#, OCaml, VB, Swift, Pascal, Fortran, Haskell, Objective-C, Assembly, HTML, CSS, JS, SQLite, Prolog.
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*******************************************************************************/
#include <bits/stdc++.h>
using namespace std;
const int N = 3e3;
int markas[N][N];
int jarak[N][N];
int jarakKiri[N][N];
bool ada = true;
int mn[N];
int mx = 0;
void solve(){
int n, m;
cin >> n >> m;
memset(jarak, 0, sizeof(jarak));
memset(jarakKiri, 0, sizeof(jarakKiri));
memset(mn, -1, sizeof(mn));
int mnPjg = n*m;
for(int i = 1; i <= n; i++){
string s;
cin >> s;
for(int j = 1; j <= m; j++){
markas[i][j] = s[j - 1] - '0';
}
}
for(int i = 1; i <= n; i++){
for(int j = m; j >= 1; j--){
jarak[i][j] = jarak[i][j + 1] + 1;
if(!markas[i][j]){
jarak[i][j] = 0;
}
}
}
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m; j++){
jarakKiri[i][j] = jarakKiri[i][j - 1] + 1;
if(!markas[i][j]){
jarakKiri[i][j] = 0;
}
}
}
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m; j++){
if(markas[i][j] == 1 && markas[i - 1][j] == 0 && markas[i][j - 1] == 0){
int k = i;
int curP = jarak[k][j];
mnPjg = min(mnPjg, curP);
while(curP != 0){
if(mn[k - i + 1] == -1){
mn[k - i + 1] = curP;
}else{
mn[k - i + 1] = min(mn[k - i + 1], curP);
}
k++;
curP = min(curP, jarak[k][j]);
}
mn[k - i + 1] = 0;
}
if(markas[i][j] == 1 && markas[i + 1][j] == 0 && markas[i][j + 1] == 0){
int k = i;
int curP = jarak[k][j];
while(curP != 0){
if(mn[i - k + 1] == -1){
mn[i - k + 1] = curP;
}else{
mn[i - k + 1] = min(mn[i - k + 1], curP);
}
k--;
curP = min(curP, jarak[k][j]);
}
mn[i - k + 1] = 0;
}
}
}
mx = mn[1];
for(int i = 2; i <= m; i++){
mn[i] = min(mn[i], mn[i - 1]);
mx = max(mx, i * mn[i]);
}
cout << mx << endl;
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(NULL);
int t;
t = 1;
while(t--){
solve();
}
return 0;
}
