A

#include <bits/stdc++.h>
// tiom4eg's precompiler options
// POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS
// IO settings
#define fastIO ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
// Quick types
#define ll long long
#define ull unsigned long long
#define pii pair <int, int>
#define vi vector <int>
#define mi vector <vector <int> >
// Quick functions
#define endl "\n"
#define F first
#define S second
#define all(a) a.begin(), a.end()
#define pb push_back
#define fint(n) int n; cin >> n
#define fstr(s) string s; cin >> s
#define farr(a, n) int a[n]; for (int pog = 0; pog < n; ++pog) cin >> a[pog]
// Quick fors
#define FOR1(s, n) for (int i = s; i < n; ++i)
#define FOR2(s, n) for (int j = s; j < n; ++j)
#define FOR3(s, n) for (int k = s; k < n; ++k)
#define RFOR(n, s) for (int l = n; l >= s; --l)
// Pragmas
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,fma")
// POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS
using namespace std;

const int MAXN = 5001;

int main() {
    fastIO;
    int n, m; cin >> n >> m;
    string g[n]; FOR1(0, n) cin >> g[i];
    int cur[MAXN], glob[MAXN]; FOR1(0, MAXN) cur[i] = 0, glob[i] = 0;
    int res = 0;
    FOR1(0, m) {
        FOR2(0, MAXN) cur[j] = 0;
        FOR2(0, n) {
            if (g[j][i] == '1') glob[j]++, cur[glob[j]]++;
            else glob[j] = 0;
        }
        RFOR(m, 0) cur[l] += cur[l + 1], res = max(res, cur[l] * l);
    }
    cout << res;
}