#include <bits/stdc++.h>
using namespace std;
template<class T, class U>
void ckmin(T &a, U b)
{
if (a > b) a = b;
}
template<class T, class U>
void ckmax(T &a, U b)
{
if (a < b) a = b;
}
#define MP make_pair
#define PB push_back
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define FOR(i, a, b) for (auto i = (a); i < (b); i++)
#define FORD(i, a, b) for (auto i = (a) - 1; i >= (b); i--)
#define SZ(x) ((int) ((x).size()))
#define ALL(x) (x).begin(), (x).end()
#define MAXN 2513
#define INF 1000000007
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pii> vpi;
typedef vector<pll> vpl;
int N, M;
bitset<MAXN> grid[MAXN];
int up[MAXN][MAXN], dn[MAXN][MAXN];
int dp[MAXN];
int ans;
int width = INF;
int32_t main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
cout << fixed << setprecision(12);
cerr << fixed << setprecision(4);
cin >> N >> M;
FOR(i, 0, N)
{
string temps; cin >> temps;
FOR(j, 0, M)
{
grid[i][j] = (temps[j] == '1');
}
}
//length of shortest vertical strip.
FOR(i, 0, M + 1)
{
dp[i] = INF;
}
// cerr << dp[2] << endl;
FOR(i, 0, M)
{
int sum = 0;
FOR(j, 0, N)
{
if (grid[j][i]) sum++;
else
{
if (sum) ckmin(dp[1], sum);
sum = 0;
}
}
if (sum) ckmin(dp[1], sum);
}
FOR(i, 0, N)
{
int sum = 0;
FOR(j, 0, M)
{
if (grid[i][j]) sum++;
else
{
if (sum) ckmin(width, sum);
sum = 0;
}
}
if (sum) ckmin(width, sum);
}
if (width >= INF)
{
cout << N * M << '\n';
return 0;
}
// cerr << dp[1] << endl;
FOR(j, 0, M)
{
FOR(i, 0, N)
{
if (!grid[i][j]) up[i][j] = i + 1;
else up[i][j] = (i == 0 ? 0 : up[i - 1][j]);
}
FORD(i, N, 0)
{
if (!grid[i][j]) dn[i][j] = i - 1;
else dn[i][j] = (i == N - 1 ? N - 1 : dn[i + 1][j]);
}
}
// FOR(i, 0, N)
// {
// FOR(j, 0, M)
// {
// cerr << up[i][j] << ' ';
// }
// cerr << endl;
// }
// FOR(i, 0, N)
// {
// FOR(j, 0, M)
// {
// cerr << dn[i][j] << ' ';
// }
// cerr << endl;
// }
FOR(i, 0, N)
{
int sum = 0; pii bound = {0, N - 1};
FOR(j, 0, M)
{
if (grid[i][j])
{
sum++;
ckmin(bound.se, dn[i][j]);
ckmax(bound.fi, up[i][j]);
}
else
{
sum = 0;
bound = {0, N - 1};
}
if (sum > 1) ckmin(dp[sum], bound.se - bound.fi + 1);
// cerr << sum << ',' << bound.se << ' ' << bound.fi << ' ' << bound.se - bound.fi + 1 << ' ';
}
// cerr << endl;
}
FOR(i, 0, N)
{
int sum = 0; pii bound = {0, N - 1};
FORD(j, M, 0)
{
if (grid[i][j])
{
sum++;
ckmin(bound.se, dn[i][j]);
ckmax(bound.fi, up[i][j]);
}
else
{
sum = 0;
bound = {0, N - 1};
}
if (sum > 1) ckmin(dp[sum], bound.se - bound.fi + 1);
// cerr << sum << ',' << bound.se - bound.fi + 1 << ' ';
}
// cerr << endl;
}
FOR(i, 1, width + 1)
{
ckmin(dp[i], dp[1]);
ckmax(ans, dp[i] * i);
// cerr << dp[i] << endl;
}
cout << ans << '\n';
return 0;
}
