#include <bits/stdc++.h>
#define pb push_back
#define sz(v) (int)v.size()
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define x first
#define y second
#define int long long
#define nl "\n"
using namespace std;
typedef long long ll;
typedef pair<long long, long long> pll;
typedef pair <ll, ll> pii;
const int N = (int)1e6 + 7;
const int M = (int)5e6 + 7;
const ll MOD = (ll)1e9 + 7;
const int inf = (int)1e9 + 7;
const ll INF = (ll)3e18 + 7;
pii dir[] = {{-1, -1}, {1, 1}, {-1, 1}, {1, -1}};
int n, m;
char c[2501][2501];
int used[2501][2501], w[2501][2501];
int get(int x1, int y1, int x2, int y2) {
return w[x2][y2] - w[x2][y1-1] - w[x1-1][y2] + w[x1-1][y1-1];
}
void upd(int x1, int y1, int x2, int y2) {
used[x1][y1]++;
used[x1][y2+1]--;
used[x2+1][y1]--;
used[x2+1][y2+1]++;
}
void solve() {
cin >> n >> m;
for(int i = 1; i <= n; ++i) {
for(int j = 1; j <= m; ++j) {
cin >> c[i][j];
w[i][j] = w[i-1][j] + w[i][j-1] - w[i-1][j-1] + (c[i][j] == '1');
}
}
int ans = inf;
if(n == 1) {
int cur = 0;
for(int i = 1; i <= m; ++i) {
if(c[1][i] == '1') cur++;
else {
if(cur > 0) ans = min(ans, cur);
cur = 0;
}
}
if(c[1][m] == '1') ans = min(ans, cur);
cout << ans << nl;
return;
}
if(m == 1) {
int cur = 0;
for(int i = 1; i <= n; ++i) {
if(c[i][1] == '1') cur++;
else {
if(cur > 0) ans = min(ans, cur);
cur = 0;
}
}
if(c[n][1] == '1') ans = min(ans, cur);
cout << ans << nl;
return;
}
ans = 0;
int l = 1, r = n;
while(l <= r) {
int e = (l + r) >> 1;
int L = 1, R = m;
bool cur = 0;
while(L <= R) {
int f = (L + R) >> 1;
for(int i = 1; i <= n; ++i) fill(used[i] + 1, used[i] + 1 + m, 0);
for(int i = 1; i <= n; ++i) {
for(int j = 1; j <= m; ++j) {
if(i + e - 1 > n || j + f - 1 > m) break;
int x = get(i, j, i + e - 1, j + f - 1);
if(x == e * f) {
upd(i, j, i + e - 1, j + f - 1);
}
}
}
for(int i = 1; i <= n; ++i) {
for(int j = 1; j <= m; ++j) {
used[i][j] += used[i-1][j] + used[i][j-1] - used[i-1][j-1];
}
}
bool ok = 1;
for(int i = 1; i <= n && ok; ++i) {
for(int j = 1; j <= m && ok; ++j) {
if(c[i][j] == '1') ok &= (used[i][j] > 0);
}
}
if(ok) {
cur = 1;
ans = max(ans, e * f);
L = f + 1;
} else
R = f - 1;
}
if(cur)
l = e + 1;
else
r = e - 1;
}
if(n <= 100 && m <= 100) {
for(int e = 1; e <= n; ++e) {
for(int f = 1; f <= n; ++f) {
bool ok = 1;
for(int i = 1; i <= n; ++i) fill(used[i] + 1, used[i] + 1 + m, 0);
for(int i = 1; i <= n; ++i) {
for(int j = 1; j <= m; ++j) {
if(i + e - 1 > n || j + f - 1 > m) break;
int x = get(i, j, i + e - 1, j + f - 1);
if(x == e * f) {
upd(i, j, i + e - 1, j + f - 1);
}
}
}
for(int i = 1; i <= n; ++i) {
for(int j = 1; j <= m; ++j) {
used[i][j] += used[i-1][j] + used[i][j-1] - used[i-1][j-1];
}
}
for(int i = 1; i <= n && ok; ++i) {
for(int j = 1; j <= m && ok; ++j) {
if(c[i][j] == '1') ok &= (used[i][j] > 0);
}
}
if(ok) {
ans = max(ans, e * f);
//cout << e << ' ' << f << nl;
}
}
}
}
cout << ans << nl;
}
signed main() {
ios_base::sync_with_stdio(NULL);
cin.tie(0);
cout.tie(0);
int test = 1;
//cin >> test;
for(int i = 1; i <= test; ++i) {
//cout << "Case " << i << ": ";
solve();
}
return 0;
}
