#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;
int cum1[MX][MX], cum2[MX][MX];
char gr[MX][MX];
int n,m;
bool ok(int x, int y) {
FOR(i,1,n+1) FOR(j,1,m+1) cum2[i][j] = 0;
F0R(i,n+1-x) F0R(j,m+1-y) if (cum1[i+x][j+y]-cum1[i][j+y]-cum1[i+x][j]+cum1[i][j] == x*y) {
cum2[i+1][j+1] ++;
cum2[i+1][j+1+y] --;
cum2[i+1+x][j+1] --;
cum2[i+1+x][j+1+y] ++;
}
FOR(i,1,n+1) FOR(j,1,m+1) {
cum2[i][j] += cum2[i][j-1]+cum2[i-1][j]-cum2[i-1][j-1];
if (gr[i][j] == '1' && !cum2[i][j]) return 0;
}
return 1;
}
int main() {
// freopen("bomb.in","r",stdin);
// freopen("bomb.out","w",stdout);
cin >> n >> m;
FOR(i,1,n+1) FOR(j,1,m+1) {
cin >> gr[i][j];
cum1[i][j] = cum1[i-1][j]+cum1[i][j-1]-cum1[i-1][j-1];
if (gr[i][j] == '1') cum1[i][j] ++;
}
int x = 0, ans = 0;
FORd(i,1,n+1) {
while (ok(i,x+1)) x ++;
ans = max(ans,i*x);
}
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
*/
