#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);
for (auto [l, r, x] : intervals) {
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
int mx = 0;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
vector <vector <int>> marked(n + 2, vector <int> (m + 2, 0));
for (auto [l, r, a, b] : rectangles) {
if (r - l + 1 < i || b - a + 1 < j) {
continue;
}
marked[l][a]++;
marked[l][b + 1]--;
marked[r + 1][a]--;
marked[r + 1][b + 1]++;
}
for (int x = 1; x <= n; x++) {
for (int y = 1; y <= m; y++) {
marked[x][y] += marked[x - 1][y] + marked[x][y - 1] - marked[x - 1][y - 1];
}
}
bool flag = 1;
for (int x = 1; x <= n; x++) {
for (int y = 1; y <= m; y++) {
if (a[x][y] == '1') {
flag &= marked[x][y] != 0;
}
}
}
if (flag) {
mx = max(mx, i * j);
}
}
}
cout << mx << '\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);
}
