#pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
#define pb push_back
#define ld long double
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define vec vector
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
mt19937_64 gen(chrono::steady_clock::now().time_since_epoch().count());
const ld eps = 1e-6;
const int mod = 998244353;
const int oo = 2e9;
const ll OO = 2e18;
const int N = 2501;
int n, m, a[N][N], pref[N][N], p[N][N];
int get(int x1, int y1, int x2, int y2)
{
return pref[x2][y2] - pref[x1 - 1][y2] - pref[x2][y1 - 1] + pref[x1 - 1][y1 - 1];
}
bool check(int h, int w)
{
for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) p[i][j] = 0;
for (int x1 = 1; x1 <= n; x1++)
{
for (int y1 = 1; y1 <= m; y1++)
{
int x2 = x1 + h - 1, y2 = y1 + w - 1;
if (x2 > n || y2 > m) break;
if (get(x1, y1, x2, y2) == h * w)
{
p[x1][y1]++;
p[x1][y2 + 1]--;
p[x2 + 1][y1]--;
p[x2 + 1][y2 + 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] += p[i][j - 1];
p[i][j] -= p[i - 1][j - 1];
if (a[i][j] == 1 && p[i][j] == 0) return false;
}
}
return true;
}
void solve()
{
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 - '0';
pref[i][j] += a[i][j];
pref[i][j] += pref[i - 1][j];
pref[i][j] += pref[i][j - 1];
pref[i][j] -= pref[i - 1][j - 1];
}
}
int ans = 0;
int ptr = m;
for (int h = 1; h <= n; h++)
{
while (ptr >= 1 && !check(h, ptr)) ptr--;
ans = max(ans, h * ptr);
}
cout << ans;
}
int32_t main()
{
// freopen("bomb.in", "r", stdin);
// freopen("bomb.out", "w", stdout);
ios_base::sync_with_stdio(false);
cin.tie(0);
solve();
return 0;
}
