#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ldb;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<ldb,ldb> pdd;
#define ff(i,a,b) for(int i = a; i <= b; i++)
#define fb(i,b,a) for(int i = b; i >= a; i--)
#define trav(a,x) for(auto& a : x)
#define sz(a) (int)(a).size()
#define fi first
#define se second
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// os.order_of_key(k) the number of elements in the os less than k
// *os.find_by_order(k) print the k-th smallest number in os(0-based)
const int mod = 1000000007;
const int inf = 1e9 + 5;
const int mxN = 2505;
int n, m;
string s[mxN];
int H[mxN][mxN];
int W[mxN][mxN];
int main(){
cin.tie(0)->sync_with_stdio(0);
cin >> n >> m;
ff(i,1,n)cin >> s[i], s[i] = " " + s[i];
ff(i,1,n){
ff(j,1,m){
if(s[i][j] == '0')continue;
int l = j;
while(l + 1 <= m && s[i][l + 1] == '1')l += 1;
int br = l - j + 1;
ff(k,j,l)W[i][k] = br;
j = l;
}
}
ff(j,1,m){
ff(i,1,n){
if(s[i][j] == '0')continue;
int l = i;
while(l + 1 <= m && s[l + 1][j] == '1')l += 1;
int br = l - i + 1;
ff(k,i,l)H[k][j] = br;
i = l;
}
}
int h = inf, w = inf;
ff(i,1,n){
ff(j,1,m){
if(s[i][j] == '1'){
h = min(h, H[i][j]);
w = min(w, W[i][j]);
}
}
}
cout << h * w << '\n';
return 0;
}
/*
// probati bojenje sahovski
*/
