#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;
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(vector<vector<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;
vector<vector<int>> sum(n, vector<int> (m));
for(int i = 0; i < n; i ++){
for(int j = 0; j < m; j ++){
if(b[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]);
}
}
for(int i = x - 1; i < n; i ++){
for(int j = y - 1; j < m; j ++){
if(SUM(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];
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;
}
}
