#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;
typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;
typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 2505;
char gr[MX][MX];
int n,m;
pi len[MX][MX];
vi temp() {
int mx = m;
vi z; F0R(i,mx+1) z.pb(MOD);
/*F0R(i,n) {
F0R(j,m) cout << gr[i][j];
cout << "\n";
}
cout << "----\n";*/
F0Rd(j,m) {
int lst = 0;
F0R(i,n) {
if (gr[i][j] == '1') {
} else {
FOR(I,lst,i) len[I][j] = {lst,i-1};
lst = i+1;
}
}
FOR(I,lst,n) len[I][j] = {lst,n-1};
F0R(i,n) {
if (gr[i][j] == '1' && (j == 0 || gr[i][j-1] == '0')) {
pi cur = {-MOD,MOD};
FOR(x,j,m+1) {
if (x == m || gr[i][x] == '0') {
mx = min(mx,x-j);
break;
}
cur.f = max(cur.f,len[i][x].f);
cur.s = min(cur.s,len[i][x].s);
z[x-j+1] = min(z[x-j+1],cur.s-cur.f+1);
}
// cout << i << " " << j << "\n";
}
}
}
FOR(i,mx+1,sz(z)) z[i] = 0;
return z;
}
vi solve() {
vi x = temp();
F0R(i,n) for (int j = 0; j < m-1-j; j++) swap(gr[i][j],gr[i][m-1-j]);
vi X = temp();
F0R(i,sz(x)) x[i] = min(x[i],X[i]);
return x;
}
int main() {
// freopen("bomb.in","r",stdin);
// freopen("bomb.out","w",stdout);
cin >> n >> m;
F0R(i,n) F0R(j,m) cin >> gr[i][j];
vi x = solve();
swap(n,m);
F0R(i,MX) FOR(j,i+1,MX) swap(gr[i][j],gr[j][i]);
vi y = solve();
int ans = 0;
F0R(i,sz(x)) F0R(j,sz(y)) if (j <= x[i] && i <= y[j]) ans = max(ans,i*j);
cout << ans;
}
/* Look for:
* the exact constraints (multiple sets are too slow for n=10^6 :( )
* special cases (n=1?)
* overflow (ll vs int?)
* array bounds
*/
