/*DavitMarg*/
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <cstring>
#include <map>
#include <unordered_map>
#include <set>
#include <queue>
#include <iomanip>
#include <bitset>
#include <stack>
#include <cassert>
#include <iterator>
#include <fstream>
#define mod 1000000007ll
#define LL long long
#define LD long double
#define MP make_pair
#define PB push_back
#define all(v) v.begin(), v.end()
using namespace std;
const int N = 2505;
int n, m, a[N][N], pr[N][N], lst[N][N], nxt[N][N];
char x;
int ans = 1;
void add(int sy, int sx, int y, int x)
{
pr[sy][sx]++;
pr[y][x]++;
pr[sy][x]--;
pr[y][sx]--;
}
int get(int sy, int sx, int y, int x)
{
return a[y][x] - a[sy - 1][x] - a[y][sx - 1] + a[sy - 1][sx - 1];
}
bool check(int k, int q)
{
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
pr[i][j] = 0;
for (int i = 1; i + k - 1 <= n; i++)
for (int j = 1; j + q - 1 <= m; j++)
if (get(i, j, i + k - 1, j + q - 1) == k * q)
add(i, j, i + k, j + q);
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];
if (get(i, j, i, j) != (bool)(pr[i][j]))
return 0;
}
return 1;
}
void solve(int k)
{
int l = max(ans / k, 1), r = m, mid;
while (l <= r)
{
mid = (l + r) / 2;
if (check(k, mid))
{
if (k * mid >= ans)
ans = k * mid;
l = mid + 1;
}
else
r = mid - 1;
}
}
int main()
{
cin >> n >> m;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
{
scanf(" %c", &x);
a[i][j] += (x - '0');
a[i][j] += a[i - 1][j] + a[i][j - 1] - a[i - 1][j - 1];
}
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
if (get(i, j, i, j))
lst[i][j] = 1 + lst[i - 1][j];
int len = n;
for (int i = n; i >= 1; i--)
for (int j = m; j >= 1; j--)
if (get(i, j, i, j))
{
nxt[i][j] = 1 + nxt[i + 1][j];
len = min(len, nxt[i][j] + lst[i][j] - 1);
}
if (n <= 450)
for (int i = 1; i <= len; i++)
solve(i);
else
solve(len);
cout << ans << endl;
return 0;
}
/*
6 6
000111
000111
001111
111100
111000
111000
*/
