#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long
#define fs first
#define ss second
#define all(a) a.begin(), a.end()
#define print(a) \
for (auto x : a) \
cout << x << ' '; \
cout << endl;
#define printmp(a) \
for (auto x : a) \
cout << x.fs << ' ' << x.ss << endl;
vector<vector<char>> a;
vector<vector<int>> sum;
int n, m;
bool check(int y)
{
for (int j = 0; j < m; j++)
{
int cnt = 0;
for (int i = 0; i < n; i++)
{
if (a[i][j] == '0')
if (cnt > 0 and cnt < y)
return false;
else
cnt = 0;
else
cnt++;
}
if (cnt > 0 and cnt < y)
return false;
}
return true;
}
bool good(int y)
{
for (int j = 0; j < n; j++)
{
int cnt = 0;
for (int i = 0; i < m; i++)
{
if (a[j][i] == '0')
if (cnt > 0 and cnt < y)
return false;
else
cnt = 0;
else
cnt++;
}
if (cnt > 0 and cnt < y)
return false;
}
return true;
}
int SUM(int i, int j, int x, int y)
{
return sum[i][j] - (i - x < 0 ? 0 : sum[i - x][j]) - (j - y < 0 ? 0 : sum[i][j - y]) + (i - x < 0 or j - y < 0 ? 0 : sum[i - x][j - y]);
}
bool f1(int x, int y)
{
vector<vector<char>> b = a;
for(int i = n - 1; i >= x - 1; i --)
for(int j = y - 1; j < m; j ++)
if (SUM(i, j, x, y) == x * y){
for (int k = 0; k < x; k++)
for (int t = 0; t < y; t++)
if (b[i - k][j - t] == '1')
b[i - k][j - t] = '2';
else
break;
}
int cnt = 0;
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
cnt += (b[i][j] == '1');
return cnt == 0;
}
void solve()
{
cin >> n >> m;
a.resize(n, vector<char>(m));
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
cin >> a[i][j];
sum.resize(n, vector<int> (m));
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
if (a[i][j] == '1')
sum[i][j] = 1;
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
sum[i][j] += (i == 0 ? 0 : sum[i - 1][j]) + (j == 0 ? 0 : sum[i][j - 1]) - (i == 0 or j == 0 ? 0 : sum[i - 1][j - 1]);
int lx = 1, rx = n;
while (lx < rx)
{
int m = (lx + rx + 1) >> 1;
if (check(m))
lx = m;
else
rx = m - 1;
}
int ly = 1, ry = m;
while (ly < ry)
{
int m = (ly + ry + 1) >> 1;
if (good(m))
ly = m;
else
ry = m - 1;
}
int LX = 1, RX = n;
while (LX < RX)
{
int m = (LX + RX + 1) >> 1;
if (f1(lx, m))
LX = m;
else
RX = m - 1;
}
int LY = 1, RY = m;
while (LY < RY)
{
int m = (LY + RY + 1) >> 1;
if (f1(m, ly))
LY = m;
else
RY = m - 1;
}
cout << max(lx * LX, ly * LY);
}
signed main()
{
ios::sync_with_stdio(0);
cin.tie(0);
// freopen("bomb.in", "r", stdin);
// freopen("bomb.out", "w", stdout);
int t = 1;
// cin >> t;
while (t--)
{
solve();
cout << endl;
}
}
