#include <bits/stdc++.h>
using namespace std;
#define int long long
#define str string
#define fastio ios::sync_with_stdio(0), cin.tie(0);
#define fs first
#define ss second
#define endl '\n'
#define all(x) (x).begin(), (x).end()
#define len(x) x.size()
#define print(a) \
for (auto &x : a) \
cout << x << " "; \
cout << endl;
#define printmp(a) \
for (auto &x : a) \
cout << x.fs << " " << x.ss << endl;
const int mod = 1e9 + 7;
void solve(){
int n, m;
cin >> n >> m;
vector<vector<char>> a(n, vector<char> (m));
for(int i = 0; i < n; i ++)
for(int j = 0; j < m; j ++)
cin >> a[i][j];
if(n <= 40 and m <= 40){
int ans = 0;
for(int i = 1; i <= n; i ++){
for(int j = 1; j <= m; j ++){
vector<vector<char>> b = a;
for(int i1 = 0; i1 <= n - i; i1 ++){
for(int i2 = 0; i2 <= m - j; i2 ++){
if(b[i1][i2] != '0'){
bool flag = 1;
for(int x = 0; x < i; x ++){
for(int y = 0; y < j; y ++){
if(b[i1 + x][i2 + y] == '0')
flag = false;
}
}
if(flag){
for(int x = 0; x < i; x ++){
for(int y = 0; y < j; y ++){
b[i1 + x][i2 + y] = '2';
}
}
}
}
}
}
int cnt = 0;
for(int i = 0; i < n; i ++){
for(int j = 0; j < m; j ++){
cnt += b[i][j] == '1';
}
}
if(cnt == 0)
ans = max(ans, i * j);
}
}
cout << ans;
return;
}
vector<vector<int>> pref(n + 1, vector<int> (m + 1));
for(int i = 0; i < n; i ++)
for(int j = 0; j < m; j ++)
pref[i + 1][j + 1] = pref[i][j + 1] + pref[i + 1][j] - pref[i][j] + (a[i][j] == '0');
vector<vector<array<int, 2>>> dp(n, vector<array<int, 2>> (m, {0, 0}));
int ans = 1;
for(int i = 1; i <= n; i ++){
for(int j = 1; j <= m; j ++){
bool flag = 1;
for(int x = 0; x < n; x ++){
for(int y = 0; y < m; y ++){
if(x + i <= n and y + j <= m and pref[x + i][y + j] - pref[x + i][y] - pref[x][y + j] + pref[x][y] == 0)
dp[x][y] = {i, j};
else{
dp[x][y] = {0, 0};
if(y > 0 and dp[x][y - 1][1] > 1)
dp[x][y] = {dp[x][y - 1][0], dp[x][y - 1][1] - 1};
else if(x > 0 and dp[x - 1][y][0] > 1)
dp[x][y] = {dp[x - 1][y][0] - 1, dp[x - 1][y][1]};
}
if(a[x][y] == '1' and dp[x][y][0] == 0 and dp[x][y][1] == 0){
flag = 0;
break;
}
}
if(!flag)
break;
}
if(flag)
ans = max(ans, i * j);
else
break;
}
}
cout << ans;
}
signed main()
{
fastio;
#ifdef Javohir
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
int t = 1;
// cin >> t;
while (t--)
{
solve();
cout << endl;
}
}
