#include <bits/stdc++.h>
#define range(i, l, r) for(long long int (i) = (l); (i) < (r); (i)++)
#define reversed_range(i, l, r) for (long long int (i) = (r) - 1; (i) >= l; (i)--)
using namespace std;
template <typename T>
using vec = vector<T>;
using lint = long long;
using ulint = unsigned long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;

template <typename S, typename T>
ostream& operator <<(ostream& os, pair<S, T> p) {
    os << "(";
    os << p.first << ", " << p.second;
    return os << ")";
}

template <typename T>
ostream& operator <<(ostream& os, vec<T> v) {
    os << "[";
    if (v.size() == 0) return os << "]";
    for (int i = 0; i < v.size() - 1; i++) {
        os << v.at(i) << ", ";
    }
    return os << v.at(v.size() - 1) << "]";
}

template <typename T>
ostream& operator <<(ostream& os, set<T>& s) {
    os << "{";
    if (s.begin() == s.end()) return os << "}";
    auto it_first_item = s.begin();
    cout << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        cout << ", " << *it;
    }
    return cout << "}";
}

template <typename T>
ostream& operator <<(ostream& os, unordered_set<T>& s) {
    os << "{";
    if (s.begin() == s.end()) return os << "}";
    auto it_first_item = s.begin();
    cout << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        cout << ", " << *it;
    }
    return cout << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    cout << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        cout << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, unordered_map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    cout << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        cout << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

lint pow(lint num, lint e, lint MOD) {
    lint res = 1;
    lint cur_num = num;
    while (e) {
        if (e & 1) {
            res *= cur_num;
            res %= MOD;
        }
        cur_num *= cur_num;
        cur_num %= MOD;
        e >>= 1;
    }
    return res;
}

int main() {
    cin.tie(0); cout.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    lint N, K; cin >> N >> K;
    vec<lint> cost(N), difficulty(N);
    range(i, 0, N) cin >> cost.at(i);
    range(i, 0, N) cin >> difficulty.at(i);
    // priority_queue<lint> cur_values;
    // range(i, 0, N) cur_values.emplace(cost.at(i));
    sort(cost.begin(), cost.end(), greater<lint>());
    sort(difficulty.begin(), difficulty.end());
    auto is_feasible = [&](lint max_cost) {
        lint num_reduced = 0;
        range(i, 0, N) {
            lint c = cost.at(i), f = difficulty.at(i);
            lint amount_over = c * f - max_cost;
            if (amount_over > 0)
                num_reduced += amount_over / f + (amount_over % f == 0 ? 0 : 1);
        }
        return num_reduced <= K;
    };
    lint cost_without_K = 0;
    range(i, 0, N) cost_without_K = max(cost_without_K, cost.at(i) * difficulty.at(i));
    lint ng = -1, ok = cost_without_K;
    // (ng, ok]
    // cout << cost << "\n";
    // cout << difficulty << "\n";
    // cout << cost_without_K << "\n";
    // cout << ng << " " << ok << "\n";
    while (ok - ng > 1) {
        lint mid = (ok + ng) / 2;
        // cout << mid << "\n";
        if (is_feasible(mid)) ok = mid;
        else ng = mid;
    }
    cout << ok << "\n";
}

Measured memory_bytes: 3328