#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define vt vector
#define f first
#define s second
#define all(x) (x).begin(), (x).end()
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define F0R(i, b) FOR(i, 0, b)
#define ROF(i, a, b) for (int i = (b) - 1; i >= (a); i--)
#define pb push_back
#define endl '\n'
#ifndef LOCAL
#define cerr if (0) std::cerr
#endif
/*
N^3: find max width for each given height
*/
int rs, cs;
vt<vt<bool>> grid;
vt<vt<int>> sfx;
int sum(int r1, int c1, int r2, int c2) {
r2 = min(r2, rs - 1);
c2 = min(c2, cs - 1);
return sfx[r1][c1] - sfx[r1][c2 + 1] - sfx[r2 + 1][c1] + sfx[r2 + 1][c2 + 1];
}
main() {
cin.tie(0)->sync_with_stdio();
cin >> rs >> cs;
rs += 2, cs += 2;
grid.resize(rs, vt<bool>(cs));
sfx.resize(rs + 1, vt<int>(cs + 1));
FOR (r, 1, rs - 1) {
FOR (c, 1, cs - 1) {
char ch; cin >> ch;
grid[r][c] = sfx[r][c] = ch - '0';
}
}
ROF (r, 0, rs) ROF (c, 0, cs) sfx[r][c] += sfx[r][c + 1];
ROF (r, 0, rs) ROF (c, 0, cs) sfx[r][c] += sfx[r + 1][c];
int mxw = cs, mxh = rs;
F0R (r, rs) {
int streak = 0;
F0R (c, cs) {
if (grid[r][c]) streak++;
else if (streak) mxw = min(mxw, streak), streak = 0;
}
}
F0R (c, cs) {
int streak = 0;
F0R (r, rs) {
if (grid[r][c]) streak++;
else if (streak) mxh = min(mxh, streak), streak = 0;
}
}
cerr << mxw << " " << mxh << endl;
int best = 0;
FOR (h, 1, mxh + 1) {
FOR (w, 1, mxw + 1) {
vt<vt<int>> pfx(rs, vt<int>(cs));
auto is_covered = [&] (int r, int c) {
return (pfx[r][c] - (r - h >= 0 ? pfx[r - h][c] : 0) - (c - w >= 0 ? pfx[r][c - w] : 0) + (r - h >= 0 && c - w >= 0 ? pfx[r - h][c - w] : 0)) > 0;
};
auto add = [&] (int r, int c) {
pfx[r][c] += (r ? pfx[r - 1][c] : 0) + (c ? pfx[r][c - 1] : 0) - (r && c ? pfx[r - 1][c - 1] : 0);
};
cerr << w << " " << h << endl;
bool good = true;
F0R (r, rs - 1) {
F0R (c, cs - 1) {
if (sum(r, c, r + h - 1, c + w - 1) == w * h) {
pfx[r][c]++;
}
add(r, c);
if (grid[r][c] == 1) {
cerr << is_covered(r, c) << endl;
good &= is_covered(r, c);
}
}
}
if (good) best = max(best, w * h);
}
}
cout << best << endl;
}
