#include <vector>
#include<iostream>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <fstream>
#include <string>
#include <set>
#include <deque>
#include <queue>
#include <map>
#include <bitset>
#include <random>
#include <cassert>
#include <unordered_map>
#include <unordered_set>
using namespace std;
typedef long long             ll;
typedef unsigned long long     ull;
typedef long double            ld;
#define endl              "\n"
#define all(a)            a.begin(), a.end()
#define allr(a)           a.rbegin(), a.rend()
#define pb                push_back
#define F                 first
#define S             second
ll inf = 1e18;
const ll c = 600;
struct point {
    ld x, y;
};

struct Vector {
    ld x, y;
    Vector(ld x_ = 0, ld y_ = 0) {
        x = x_;
        y = y_;
    }
    Vector(point& a, point& b) {
        x = b.x - a.x;
        y = b.y - a.y;
    }
};
const ll mod = 1e9 + 7;
template<typename T>
T SUM(T x) {
    return x;
}
template<typename T, typename... Ts>
T SUM(T x, Ts... y) {
    T res = x + SUM(y...);
    if (res >= mod)
        res -= mod;
    return res;
}
template<typename T, typename... Ts>
T sub(T x, Ts... y) {
    return SUM(x, mod - SUM(y...));
}
template<typename T>
T proiz(T x) {
    return x;
}
template<typename T, typename... Ts>
T proiz(T x, Ts... y) {
    return (x * 1ll * proiz(y...)) % mod;
}
template<typename T, typename... Ts>
void prisvoenie_proiz(T& x, Ts... y) {
    x = proiz(x, y...);
}
ll bin(ll a, ll deg) {
    ll r = 1;
    while (deg) {
        if (deg & 1)
            prisvoenie_proiz(r, a);
        deg >>= 1;
        prisvoenie_proiz(a, a);
    }
    return r;
}
ll inv(ll x) {
    return bin(x, mod - 2);
}
void solve() {
    ll n, m;
    cin >> m >> n;
    vector<vector<ll>> a(m, vector<ll>(n));
    for (ll i = 0; i < m; i++) {
        for (ll j = 0; j < n; j++) {
            cin >> a[i][j];
        }
    }
    vector <ll> h(n + 2,0);
    ll mxans = -inf;
    for (ll j = 0; j < m; j++) {
        h[0] = -inf;
        h[n + 1] = -inf;
        for (ll i = 1; i <= n; i++) {
            if (!a[j][i - 1]) {
                h[i]++;
            }
            else {
                h[i] = 0;
            }
        }
        vector <ll> stack1(1, 0), stack2(1, n + 1), ans1(n + 2), ans2(n + 2);
        for (ll i = 1; i < n + 2; i++) {
            while (h[stack1.back()] > h[i]) {
                ans1[stack1.back()] = i;
                stack1.pop_back();
            }
            stack1.push_back(i);
        }
        for (ll i = n + 1; i >= 1; i--) {
            while (h[stack2.back()] > h[i]) {
                ans2[stack2.back()] = i;
                stack2.pop_back();
            }
            stack2.push_back(i);
        }
        ll anss = -inf;
        for (ll i = 1; i <= n; i++) {
            anss = max(anss, h[i] * (ans1[i] - 1 - (ans2[i] + 1) + 1));
        }
        mxans = max(anss, mxans);
    }
    cout << mxans << endl;
}
signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    ll t = 1;
    //cin >> t;
    while (t--) {
        solve();
    }
}