#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define ld long double
#define ff first
#define ss second
#define ln "\n"
#define mp make_pair
const ll INF = 2e18;
const ll MOD = 1e9+7;
void solve(){
ll n, m; cin >> n >> m;
vector<vector<ll>> a(n+1, vector<ll>(m+1));
for (ll i=1; i<=n; i++){
for (ll j=1; j<=m; j++){
char x; cin >> x; a[i][j]=x-'0';
}
}
vector<vector<ll>> wl(n+1, vector<ll>(m+1)), wr(n+1, vector<ll>(m+1));
for (ll i=1; i<=n; i++){
for (ll j=1; j<=m; j++){
if (a[i][j]) wl[i][j]=wl[i][j-1]+1;
}
for (ll j=m; j>=1; j--){
if (a[i][j]) wr[i][j]=1;
if (j+1<=m) wr[i][j]+=wr[i][j+1];
}
}
vector<ll> h(n+1, INF), ah(n+1);
for (ll j=1; j<=m; j++){
ll exist=0;
for (ll i=1; i<=n; i++){
if (a[i][j]) exist=1;
}
if (!exist) continue;
ll l=INF, r=INF, hcnt=0;
ah.assign(n+1, INF);
for (ll i=1; i<=n; i++){
if (a[i][j]){
l=min(l, wl[i][j]); r=min(r, wr[i][j]);
hcnt++;
ah[hcnt]=min(ah[hcnt], l+r-1);
// cout << i << "-" << j << ": " << hcnt << "-" << l+r-1 << ln;
}else{
l=INF; r=INF; hcnt=0;
}
}
l=INF; r=INF; hcnt=0;
for (ll i=n; i>=1; i--){
if (a[i][j]){
l=min(l, wl[i][j]); r=min(r, wr[i][j]);
hcnt++; ah[hcnt]=min(ah[hcnt], l+r-1);
}else{
l=INF; r=INF; hcnt=0;
}
}
for (ll i=1; i<=n; i++){
h[i]=min(h[i], (ah[i]==INF?0:ah[i]));
}
}
ll res=0;
for (ll i=1; i<=n; i++){
if (h[i]==INF) continue;
res=max(res, i*h[i]);
}
cout << res << ln;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
auto start = chrono::high_resolution_clock::now();
ll t=1;
// cin >> t;
while (t--) solve();
#ifdef LOCAL
auto duration = chrono::duration_cast<chrono::microseconds>(chrono::high_resolution_clock::now() - start);
cout << setprecision(0) << fixed << "time: " << (double)duration.count()/1000.0 << " milliseconds" << endl;
#endif
}
