#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
/*
0011
0011
1110
1100
*/
vector <array <int, 3>> get (vector <int> c) {
int n = c.size() - 1;
vector <int> nxt(n + 1, n + 1), prv(n + 1, 0);
vector <int> cur;
for (int i = 1; i <= n; i++) {
while (!cur.empty() && c[cur.back()] >= c[i]) {
nxt[cur.back()] = i;
cur.pop_back();
}
cur.push_back(i);
}
cur.clear();
for (int i = n; i >= 1; i--) {
while (!cur.empty() && c[cur.back()] > c[i]) {
prv[cur.back()] = i;
cur.pop_back();
}
cur.push_back(i);
}
vector <array <int, 3>> ret;
for (int i = 1; i <= n; i++) {
ret.push_back({prv[i] + 1, nxt[i] - 1, c[i]});
}
return ret;
}
void solve (int X) {
int n, m; cin >> n >> m;
vector <vector <char>> a(n + 1, vector <char> (m + 1));
vector <vector <int>> up(n + 1, vector <int> (m + 1, 0));
vector <vector <int>> down(n + 2, vector <int> (m + 1, 0));
vector <vector <int>> f(n + 2, vector <int> (m + 1, 0));
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> a[i][j];
}
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
up[i][j] = (a[i][j] == '0' ? 0 : 1 + up[i - 1][j]);
}
}
for (int i = n; i >= 1; i--) {
for (int j = 1; j <= m; j++) {
down[i][j] = (a[i][j] == '0' ? 0 : 1 + down[i + 1][j]);
}
}
int mn = n;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
f[i][j] = up[i][j] + down[i][j] - 1;
if (a[i][j] == '1') {
mn = min(mn, f[i][j]);
}
}
}
vector <array <int, 4>> rectangles;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (a[i][j] == '0') {
continue;
}
int k = j;
while (k + 1 <= m && a[i][k + 1] == '1') {
k++;
}
vector <int> c = {0};
for (int l = j; l <= k; l++) {
c.push_back(down[i][l]);
}
auto intervals = get(c);
vector <int> pref = {0};
for (int l = j; l <= k; l++) {
pref.push_back(pref.back() + (up[i][l] == 1));
}
for (auto [l, r, x] : intervals) {
if (pref[r] - pref[l - 1] == 0) {
continue;
}
rectangles.push_back({i, i + x - 1, j - 1 + l, j - 1 + r});
}
j = k;
}
}
/* for (auto [l, r, a, b] : rectangles) {
cout << l << " " << r << " " << a << " " << b << '\n';
}*/
//Choose (x, y) such that every 1 cell is covered by a rectangle with dx >= x and dy >= y
//Iterate over rectangles in decreasing order of dx and maintain for each cell the maximum dy for it
//Then you want minimum value for all cells
//You want to do this update quickly for the rectangle
//It is just a range set operation
int ans = 0;
vector <vector <int>> mx(n + 2, vector <int> (m + 2, 0));
vector <int> nxt(n + 1, m);
for (int j = 1; j <= m; j++) {
vector <array <int, 3>> ee[n + 1];
for (auto [l, r, a, b] : rectangles) {
if (a <= j && j <= b) {
ee[r - l + 1].push_back({l, r, b - a + 1});
}
}
vector <int> cur(n + 1, 0);
for (int x = n; x >= 1; x--) {
for (auto [l, r, k] : ee[x]) {
for (int i = l; i <= r; i++) {
cur[i] = k;
}
}
int mn = m;
for (int i = 1; i <= n; i++) {
if (a[i][j] == '1') {
mn = min(mn, cur[i]);
}
}
nxt[x] = min(nxt[x], mn);
}
}
for (int i = 2; i <= n; i++) {
nxt[i] = min(nxt[i - 1], nxt[i]);
}
for (int i = n; i >= 1; i--) {
ans = max(ans, i * nxt[i]);
}
cout << ans << '\n';
}
signed main () {
#ifndef ONLINE_JUDGE
// freopen("input_file", "r", stdin);
//freopen("output_file", "w", stdout);
#endif
ios::sync_with_stdio(0); cin.tie(0);
int tc = 1; //cin >> tc;
for (int i = 1; i <= tc; i++) solve(i);
}
