//#pragma GCC optimize("O3,unroll-loops")
//#pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define ui unsigned int
#define ld long double
#define pl pair<long long int, long long int>
#define boost ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define ff first
#define ss second
#define sz size()
#define all(x) x.begin(), x.end()
using namespace std;
const int maxn = 1e6 + 11;
const int inf = 1e17 + 1;
const int mod = 1e9 + 7;
// const int mod = 998244353;
const int dx[] = {-1, 0, 0, 1, -1, -1, 1, 1};
const int dy[] = {0, -1, 1 , 0, -1, 1, -1, 1};
const double eps = 1e-10;
int n, m;
int pr[2505][2505], p[2505][2505];
void solve() {
cin >> n >> m;
char ch[n + 5][m + 5];
int cnt = 0;
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= m; j++) {
cin >> ch[ i ][ j ];
}
}
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= m; j++) {
pr[ i ][ j ] = pr[i - 1][ j ] + pr[ i ][j - 1] - pr[i - 1][j - 1] + (ch[ i ][ j ] - '0');
}
}
int y = m;
int x = 1;
int ans = 0;
while(x <= n && y) {
int l = 1, r = y;
int anss = 0;
while(l <= r) {
int mid = l + r >> 1;
for(int i = 0; i <= n; i++) {
for(int j = 0; j <= m; j++) {
p[ i ][ j ] = 0;
}
}
for(int i = 0; i + x <= n; i++) {
for(int j = 0; j + mid <= m; j++) {
int c = pr[i + x][j + mid] - pr[i + x][ j ] - pr[ i ][j + mid] + pr[ i ][ j ];
if(c == x * mid) {
p[i + x + 1][j + mid + 1]++;
p[i + 1][j + mid + 1]--;
p[i + x + 1][j + 1]--;
p[i + 1][j + 1]++;
}
}
}
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= m; j++) {
p[ i ][ j ] += p[i - 1][ j ] + p[ i ][j - 1] - p[i - 1][j - 1];
}
}
bool fl = true;
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= m; j++) {
if(ch[ i ][ j ] == '1' && p[ i ][ j ] == 0) {
fl = false;
break;
}
}
}
if(fl) {
anss = mid;
l = mid + 1;
}
else {
r = mid - 1;
}
}
y = anss;
ans = max(ans, x * y);
x++;
}
cout << ans;
}
signed main() {
// freopen("sum.in", "r", stdin);
// freopen("sum.out", "w", stdout);
boost;
int tt = 1;
// cin >> tt;
for(int i = 1; i <= tt; i++) {
// cout << "Case " << i << ":\n";
solve();
}
}
