#include<bits/stdc++.h>
using namespace std;
// // PBDS Template
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//using namespace __gnu_pbds;
//
//template <class T>
//using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
//using ordered_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag,tree_order_statistics_node_update>;
// Preset
const int maxn = 10000;
const int INF = INT_MAX;
const long long int LINF = LLONG_MAX;
const long long int mod = 1e9 + 7;
const long long int mod2 = 998244353;
//const double e = 2.71828;
const double PI = acos(-1);
const double eps = 1e-10;
#define pb push_back
#define ll long long
#define ull unsigned long long
typedef pair<char,char> pc;
typedef pair<double,double> pd;
typedef pair<int,int> pi;
typedef pair<ll,ll> pll;
typedef pair<pi,int> pii;
typedef pair<int,ll> pil;
typedef pair<ll,int> pli;
typedef pair<string,int> psi;
typedef pair<int,string> pis;
typedef pair<char,int> pci;
typedef pair<int,char> pic;
typedef pair<int,double> pid;
typedef pair<double,int> pdi;
int dr[4] = {0,1,0,-1}, dc[4] = {1,0,-1,0};
int t[maxn+5][maxn+5], lazy[maxn+5][maxn+5];
// build
void build(int i, vector<int> &a, int v, int st, int en) {
if (st == en) {
t[i][v] = a[st];
return;
}
int mid = (st + en) / 2;
build(i, a, 2*v, st, mid);
build(i, a, 2*v+1, mid + 1, en);
t[i][v] = t[i][2*v] + t[i][2*v+1];
}
// update
void update(int i, int v, int st, int en, int l, int r, int val) {
if (lazy[v] != 0) {
t[i][v] = (en - st + 1) * lazy[i][v];
if (st != en) {
lazy[i][2*v] = lazy[i][v];
lazy[i][2*v+1] = lazy[i][v];
}
lazy[i][v] = 0;
}
if ((en < l) || (st > r)) {
return;
}
if (st >= l && en <= r) {
t[i][v] = (en - st + 1) * val;
if (st != en) {
lazy[i][2*v] = val;
lazy[i][2*v+1] = val;
}
return;
}
int mid = (st + en) / 2;
update(i,2*v, st, mid, l, r, val);
update(i,2*v+1, mid + 1, en, l, r, val);
t[i][v] = (t[i][2*v] + t[i][2*v+1]);
}
// query
int query(int i, int v, int st, int en, int l, int r) {
if (lazy[v] != 0) {
t[i][v] = (en - st + 1) * lazy[i][v];
if (st != en) {
lazy[i][2*v] = lazy[i][v];
lazy[i][2*v+1] = lazy[i][v];
}
lazy[i][v] = 0;
}
if (en < l || st > r) {
return 0;
}
if ((l <= st) && (en <= r)) {
return t[i][v];
}
int mid = (st + en) / 2;
ll q1 = query(i, 2*v, st, mid, l, r);
ll q2 = query(i, 2*v+1, mid + 1, en, l, r);
return (q1 + q2);
}
void solve() {
int n,m;
cin >> n >> m;
string s[n+5];
for (int i=0; i<n; i++) {
cin >> s[i];
}
vector<vector<int>> a(n+1, vector<int>(m+1)), b(m+1, vector<int>(n+1)), ps(n+1, vector<int>(m+1,0));
for (int i=0; i<n; i++) {
for (int j=0; j<m; j++) {
a[i+1][j+1] = (int)(s[i][j] - '0');
}
}
for (int i=0; i<m; i++) {
for (int j=0; j<n; j++) {
b[i+1][j+1] = (int)(s[j][i] - '0');
}
}
for (int i=1; i<=n; i++) ps[i][1] = a[i][1];
for (int i=1; i<=m; i++) ps[1][i] = a[1][i];
for (int i=2; i<=n; i++) {
for (int j=2; j<=m; j++) {
ps[i][j] = ps[i][j-1] + ps[i-1][j] - ps[i-1][j-1] + a[i][j];
}
}
int h = 0, w = 0;
// binser for height
int l = 1, r = n;
while (l<=r) {
int mid = l + (r-l)/2;
for (int i=1; i<=m; i++) {
build(i,b[i],1,1,n);
}
for (int i=1; i<=m; i++) {
for (int j=1; j<=n-mid; j++) {
int area = ps[j+mid][i] - ps[j-1][i];
if (area == mid) {
update(i,1,1,n,j,j+mid,0);
}
}
}
int sum = 0;
for (int i=1; i<=m; i++) sum += query(i,1,1,n,1,n);
cout << "height = " << mid << ' ' << sum << endl;
if (sum==0) {
h = max(h, mid);
l = mid+1;
}
else r = mid-1;
}
// binser for width
l = 1, r = m;
while (l<=r) {
int mid = l + (r-l)/2;
for (int i=1; i<=n; i++) {
build(i,a[i],1,1,m);
for (int j=1; j<=m; j++) cout << query(i,1,1,m,j,j) << ' ';
cout << endl;
}
cout << endl;
for (int i=1; i<=n; i++) {
for (int j=1; j<=m-mid; j++) {
int area = ps[i][j+mid] - ps[i][j-1];
if (area == mid) {
update(i,1,1,m,j,j+mid,0);
}
}
}
for (int i=1; i<=n; i++) {
for (int j=1; j<=m; j++) cout << query(i,1,1,m,j,j) << ' ';
cout << endl;
}
int sum = 0;
for (int i=1; i<=m; i++) sum += query(i,1,1,m,1,m);
cout << "width = " << mid << ' ' << sum << endl;
if (sum==0) {
w = max(w, mid);
l = mid+1;
}
else r = mid-1;
}
int ans = h*w;
cout << ans << endl;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
// precompute();
// FFT::init_fft();
int tc=1;
// cin >> tc;
// getchar();
// int idx = 0;
while (tc--) solve();
return 0;
}
