#include <bits/stdc++.h>
//#pragma GCC optimize("unroll-loops")
//#pragma GCC optimize("-O3")
//#pragma GCC optimize("Ofast")
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define sz(x) ((int)x.size())
#define MP make_pair
#define ft first
#define sd second
#define pii pair<int, int>
#define PB push_back
using namespace std;
using namespace __gnu_pbds;
typedef long double ld;
typedef long long ll;
template <class T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int N = 2510;
const int oo = 2e9;
int n, m, ans, a[N][N], mx = oo, pref[N][N], an1;
short pr[N][N], best[N], nt[N][N], down[N][2], up[N][2];
int pl[N][N], vl[N][N];
stack<int> st;
bool ok(int ht, int wd){
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
pl[i][j] = 0;
bool was = 1;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++){
if (i + ht - 1 > n || j + wd - 1 > m)
break;
int i1 = i + ht - 1, i2 = i - 1;
int j1 = j + wd - 1, j2 = j - 1;
int kol = pref[i1][j1] - pref[i2][j1] - pref[i1][j2] + pref[i2][j2];
if (kol > 0) continue;
was = 1;
pl[i][j]++; pl[i][j + wd]--;
pl[i + ht][j]--; pl[i + ht][j + wd]++;
}
if (!was) return 0;
for (int i = 1; i <= n; i++){
int cr = 0;
for (int j = 1; j <= m; j++){
cr += pl[i][j];
vl[i][j] = cr;
}
}
for (int j = 1; j <= m; j++){
int cr = 0;
for (int i = 1; i <= n; i++){
cr += vl[i][j];
if (a[i][j] == 1 && cr == 0)
return 0;
}
}
return 1;
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0);
// freopen("in.txt","r",stdin);
ll sta = chrono::system_clock().now().time_since_epoch().count();
cin >> n >> m;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++){
char c; cin >> c;
a[i][j] = (c == '1' ? 1 : 0);
pref[i][j] = (a[i][j] ^ 1) + pref[i - 1][j] + pref[i][j - 1] - pref[i - 1][j - 1];
}
for (int j = 1; j <= m; j++){
for (int i = 1; i <= n; ){
if (a[i][j] == 0)
i++;
else {
int i1 = i;
while (i1 <= n && a[i1][j] == 1)
i1++;
mx = min(mx, i1 - i);
i = i1;
}
}
}
if (mx == oo){
cout << n * m;
return 0;
}
fill(best, best + n + 1, N);
for (int i = 1; i <= n; i++){
int pre = 0;
for (int j = 1; j <= m; j++){
if (a[i][j] == 0)
pre = j;
pr[i][j] = pre + 1;
}
pre = m + 1;
for (int j = m; j > 0; j--){
if (a[i][j] == 0)
pre = j;
nt[i][j] = pre - 1;
}
}
for (int j = 1; j <= m; j++){
for (int i = 1; i <= n; ){
if (a[i][j] == 0)
i++;
else {
int i1 = i;
while (i1 <= n && a[i1][j] == 1)
i1++;
while (sz(st)) st.pop();
for (int ii = i; ii < i1; ii++){
while (sz(st) && pr[st.top()][j] <= pr[ii][j])
st.pop();
down[ii][0] = (sz(st) == 0 ? i : st.top() + 1);
st.push(ii);
}
while (sz(st)) st.pop();
for (int ii = i; ii < i1; ii++){
while (sz(st) && nt[st.top()][j] >= nt[ii][j])
st.pop();
down[ii][1] = (sz(st) == 0 ? i : st.top() + 1);
st.push(ii);
}
while (sz(st)) st.pop();
for (int ii = i1 - 1; ii >= i; ii--){
while (sz(st) && pr[st.top()][j] <= pr[ii][j])
st.pop();
up[ii][0] = (sz(st) == 0 ? i1 - 1 : st.top() - 1);
st.push(ii);
}
while (sz(st)) st.pop();
for (int ii = i1 - 1; ii >= i; ii--){
while (sz(st) && nt[st.top()][j] >= nt[ii][j])
st.pop();
up[ii][1] = (sz(st) == 0 ? i1 - 1 : st.top() - 1);
st.push(ii);
}
i = i1;
}
}
for (int i = 1; i <= n; i++){
if (a[i][j] == 0) continue;
int l = max(down[i][0], down[i][1]);
int r = min(up[i][0], up[i][1]);
int cur = r - l + 1;
best[cur] = min(best[cur], short(nt[i][j] - pr[i][j] + 1));
}
}
best[n + 1] = N;
for (int i = n; i > 0; i--) {
best[i] = min(best[i + 1], best[i]);
if (best[i] < N && i <= mx)
ans = max(ans, int(best[i]) * i);
}
bool full = 1;
int wd = m;
for (int ht = 1; ht <= n; ht++){
ll tim = chrono::system_clock().now().time_since_epoch().count();;
if (tim - sta > ll(1e9) - ll(3e8)) {
full = 0;
break;
}
while (wd > 0 && !ok(ht, wd))
wd--;
if (wd == 0)
break;
if (n * wd <= an1)
break;
an1 = max(an1, ht * wd);
}
// if (!full) return -1;
if (full)
cout << an1;
else cout << max(ans, an1);
return 0;
}
