/*
Code written by Talant I.D.
*/
#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
//typedef tree <int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> indexed_set;
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
#define precision(n) fixed << setprecision(n)
#define pb push_back
#define ub upper_bound
#define lb lower_bound
#define mp make_pair
#define eps (double)1e-9
#define PI 2*acos(0.0)
#define endl "\n"
#define sz(v) int((v).size())
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define do_not_disturb ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define OK cout << "OK" << endl;
inline bool isvowel(char ch){
ch = tolower(ch);
return (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u');
}
inline bool isprime(int n){
if(n < 2 || (n%2 == 0 && n != 2)) return false;
for(int i = 3; i*i <= n; i++)
if(n%i == 0) return false;
return true;
}
class Union{
private:
vector <int> saizu, link;
public:
Union(int n){
saizu.assign(n, 1); link.resize(n);
iota(all(link), 0);
}
int find(int n){
if(link[n] == n) return n;
return link[n] = find(link[n]);
}
int same(int a, int b){
return find(a) == find(b);
}
void unite(int a, int b){
if(same(a, b)) return;
a = find(a); b = find(b);
if(saizu[a] < saizu[b]) swap(a, b);
saizu[a] += saizu[b];
link[b] = a;
}
int getsize(int a){
return saizu[find(a)];
}
};
const int mod = 1e9+7;
ll mode(ll a){
a %= mod;
if(a < 0) a += mod;
return a;
}
ll subt(ll a, ll b){
return mode(mode(a)-mode(b));
}
ll add(ll a, ll b){
return mode(mode(a)+mode(b));
}
ll mult(ll a, ll b){
return mode(mode(a)*mode(b));
}
ll binpow(ll a, ll b){
ll res = 1;
while(b){
if(b&1) res = mult(res, a);
a = mult(a, a);
b >>= 1;
}
return res;
}
int main(){
do_not_disturb
int n, m, i, j;
cin >> n >> m;
int grid[n+1][m+1], pref[n+2][m+2], suff[n+2][m+2], up[n+2][m+2], down[n+2][m+2];
for(i = 1; i <= n; i++){
pref[i][0] = 0;
suff[i][m+1] = m+1;
for(j = 1; j <= m; j++){
up[0][j] = 0;
down[n+1][j] = n+1;
char ch;
cin >> ch;
grid[i][j] = ch-'0';
}
}
for(i = 1; i <= n; i++){
for(j = 1; j <= m; j++){
if(grid[i][j]) pref[i][j] = pref[i][j-1];
else pref[i][j] = j;
}
for(j = m; j; j--){
if(grid[i][j]) suff[i][j] = suff[i][j+1];
else suff[i][j] = j;
}
}
for(j = 1; j <= m; j++){
for(i = 1; i <= n; i++){
if(grid[i][j]) up[i][j] = up[i-1][j];
else up[i][j] = i;
}
for(i = n; i; i--){
if(grid[i][j]) down[i][j] = down[i+1][j];
else down[i][j] = i;
}
}
vector <int> res(m+1, 2e9);
for(i = 1; i <= n; i++){
int mnu = 2e9, mnd = 2e9;
for(j = 1; j <= m; j++){
if(grid[i][j]){
mnu = min(mnu, i-up[i][j]);
mnd = min(mnd, down[i][j]-i);
res[j-pref[i][j]] = min(res[j-pref[i][j]], (mnu+mnd-1));
}
else{
mnu = mnd = 2e9;
}
}
mnu = mnd = 2e9;
for(j = m; j; j--){
if(grid[i][j]){
mnu = min(mnu, i-up[i][j]);
mnd = min(mnd, down[i][j]-i);
res[suff[i][j]-j] = min(res[suff[i][j]-j], (mnu+mnd-1));
}
else{
mnu = mnd = 2e9;
}
}
}
int to_consider = 2e9;
for(i = 1; i <= n; i++){
for(j = 1; j <= m; j++){
if(grid[i][j]){
to_consider = min(to_consider, suff[i][j]-pref[i][j]-1);
}
}
}
int ans = 0;
for(j = 1; j <= to_consider; j++){
ans = max(ans, res[j]*j);
}
cout << ans;
return 0;
}
