#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define per(i, b, a) for(int i = b - 1; i >= a; i--)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef long double ld;
typedef unsigned long long ull;
unsigned seed = chrono::system_clock::now().time_since_epoch().count();
mt19937 eng(seed);
ll random2(){
return (1ll << 31ll)*eng()+eng();
}
ll n,m,k,q,T;
const ll big = 1000000007;
const ll big2 = 1000000009;
const ll mod = 998244353;
const int MAXN = 2501;
bool grid[MAXN][MAXN] = {0};
bool covered[MAXN][MAXN] = {0};
int CS[MAXN][MAXN] = {0};
int sum(int i1, int j1, int i2, int j2){
return CS[i2+1][j2+1] - CS[i1][j2+1] - CS[i2+1][j1] + CS[i1][j1];
}
bool can_place(int i, int j, int a, int b){
if(n-i < a || m-j < b)return 0;
return (sum(i,j,i+a-1,j+b-1) == 0);
rep(c1,0,a){
rep(c2,0,b){
if(!grid[i+c1][j+c2])return 0;
}
}
return 1;
}
bool can_cover(int i, int j, int a, int b){
rep(dx,0,a){
rep(dy,0,b){
int i2 = i - dx;
int j2 = j - dy;
if(i2 >= 0 && j2 >= 0 && can_place(i2,j2,a,b))return 1;
}
}
return 0;
}
bool solve(int a, int b){
rep(c1,0,n){
rep(c2,0,m){
if(grid[c1][c2] && (c1 == n-1 || !grid[c1+1][c2] || c1 == 0 || !grid[c1-1][c2]) && !can_cover(c1,c2,a,b))return 0;
}
}
return 1;
}
int lft[MAXN][MAXN] = {0};
int up[MAXN][MAXN] = {0};
int mina = big;
int minb = big;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
// freopen("fhc.txt","r",stdin);
// freopen("autput.txt","w",stdout);
ll a,b,c,d,e;
cin >> n >> m;
rep(c1,0,n){
string s;
cin >> s;
rep(c2,0,m){
grid[c1][c2] = (s[c2] == '1');
}
}
rep(c1,1,n+1){
rep(c2,1,m+1){
CS[c1][c2] = (!grid[c1-1][c2-1]) + CS[c1-1][c2] + CS[c1][c2-1] - CS[c1-1][c2-1];
}
}
rep(c1,0,n){
rep(c2,0,m){
if(grid[c1][c2]){
if(c1 == 0){
up[c1][c2] = 1;
}
else{
up[c1][c2] = up[c1-1][c2]+1;
}
if(c1 == n-1 || !grid[c1+1][c2])mina = min(mina, up[c1][c2]);
if(c2 == 0){
lft[c1][c2] = 1;
}
else{
lft[c1][c2] = lft[c1][c2-1]+1;
}
if(c2 == m-1 || !grid[c1][c2+1])minb = min(minb, lft[c1][c2]);
}
}
}
ll ans = 0;
rep(a,1,mina+1){
int lo = 1;
int hi = minb+1;
while(lo < hi-1){
int mid = (lo+hi)/2;
if(solve(a, mid)){
lo = mid;
}
else{
hi = mid;
}
}
ans = max(ans, ll(a)*ll(lo));
}
cout << ans << "\n";
return 0;
}
