# include <stdio.h>
# include <bits/stdc++.h>
#define _USE_MATH_DEFINES_
#define ll long long
#define ld long double
#define Accepted 0
#define pb push_back
#define mp make_pair
#define sz(x) (int)(x.size())
#define every(x) x.begin(),x.end()
#define F first
#define S second
#define For(i,x,y) for (int i = x; i <= y; i ++)
#define FOr(i,x,y) for (int i = x; i >= y; i --)
#define SpeedForce ios_base::sync_with_stdio(0), cin.tie(0)
// ROAD to... Red
using namespace std;
inline bool isvowel (char c) {
c = tolower(c);
if (c == 'a' || c == 'e' || c == 'i' || c == 'y' || c == 'o' || c == 'u') return 1;
return 0;
}
const double eps = 0.000001;
const ld pi = acos(-1);
const int maxn = 1e7 + 9;
const int mod = 1e9 + 7;
const ll MOD = 1e18 + 9;
const ll INF = 1e18 + 123;
const int inf = 2e9 + 11;
const int mxn = 1e6 + 9;
const int N = 6e5 + 123;
const int M = 22;
const int pri = 997;
const int Magic = 2101;
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, -1, 0, 1};
short n, m;
bool a[2530][2530];
short l[2530][2530];
short r[2530][2530];
int f[2503];
int main () {
SpeedForce;
cin >> n >> m;
int ans = 0;
int w = inf, h = inf;
For (i, 1, n) {
For (j, 1, m) {
char c;
cin >> c;
a[i][j] = c - '0';
if (a[i][j] == 0) l[i][j] = j;
else l[i][j] = l[i][j - 1];
}
r[i][m + 1] = m + 1;
FOr(j, m, 1) {
if (a[i][j] == 0) r[i][j] = j;
else {
r[i][j] = r[i][j + 1];
w = min(w, (int)r[i][j] - l[i][j] - 1);
}
}
}
For (j, 1, m) {
For (i, 1, n) {
if (a[i][j] == 0) l[i][j] = i;
else l[i][j] = l[i - 1][j];
}
r[n + 1][j] = n + 1;
FOr(i, n, 1) {
if (a[i][j] == 0) r[i][j] = i;
else {
r[i][j] = r[i + 1][j];
h = min(h, (int) r[i][j] - l[i][j] - 1);
}
}
}
For (i, 1, w) f[i] = h;
For (i, 1, n) {
int cur = 0;
For (j, 1, m) {
if (a[i][j] == 0) cur =0;
else {
cur ++;
f[cur] = min(f[cur], r[i][j] - l[i][j] - 1);
}
}
}
For (i, 1, w) ans = max(ans, f[i] * i);
cout << ans;
return Accepted;
}
// Coded By OB
