#include "bits/stdc++.h"
using namespace std;
using ll = long long;
using vll = std::vector<ll>;
using vvll = std::vector<vll>;
using vvvll = std::vector<vvll>;
using dd = double;
using vdd = std::vector<dd>;
using vvdd = std::vector<vdd>;
using vvvdd = std::vector<vvdd>;

constexpr ll INF = 1LL << 60;
constexpr ll MOD = (ll)(1e9 + 7);// 998244353L;
constexpr dd EPS = 1e-11;

typedef std::numeric_limits< double > dbl;

//cin,cout高速化のおまじない＋桁数指定
struct Fast{
	Fast(){
		cin.tie(0);
		ios::sync_with_stdio(false);
		cout << fixed << setprecision(std::numeric_limits<double>::max_digits10);
	}
} fast;

#define REPS(i, S, E) for (ll i = (S); i <= (E); i++)
#define REP(i, N) REPS(i, 0, N-1)
#define DEPS(i, E, S) for (ll i = (E); i >= (S); i--)
#define DEP(i, N) DEPS(i, N-1, 0)
#define EACH(e, v) for (auto&& e : v)

template<class T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; }return false; }
template<class T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; }return false; }
template<class T> inline T MaxE(vector<T> &v, ll S, ll E){ T m=v[S]; REPS(i, S, E)chmax(m, v[i]); return m; }//v[S]～v[E]の最大値
template<class T> inline T MinE(vector<T> &v, ll S, ll E){ T m=v[S]; REPS(i, S, E)chmin(m, v[i]); return m; }//v[S]～v[E]の最小値
template<class T> inline T MaxE(vector<T> &v, ll N) { return MaxE(v, 0, N - 1); } //先頭N個中の最大値
template<class T> inline T MinE(vector<T> &v, ll N) { return MinE(v, 0, N - 1); }
template<class T> inline T MaxE(vector<T> &v) { return MaxE(v, (ll)v.size()); }
template<class T> inline T MinE(vector<T> &v) { return MinE(v, (ll)v.size()); }
template<class T> inline ll MaxI(vector<T> &v, ll S, ll E){ ll m=S; REPS(i, S, E){ if (v[i]>v[m])m=i; }return m; }
template<class T> inline ll MinI(vector<T> &v, ll S, ll E){ ll m=S; REPS(i, S, E){ if (v[i]<v[m])m=i; }return m; }
template<class T> inline ll MaxI(vector<T> &v, ll N) { return MaxI(v, 0, N - 1); }
template<class T> inline ll MinI(vector<T> &v, ll N) { return MinI(v, 0, N - 1); }
template<class T> inline ll MaxI(vector<T> &v) { return MaxI(v, (ll)v.size()); }
template<class T> inline ll MinI(vector<T> &v) { return MinI(v, (ll)v.size()); }
template<class T> inline T Sum(vector<T> &v, ll S, ll E){ T s=v[S]; REPS(i, S+1, E)s+=v[i]; return s; }
template<class T> inline T Sum(vector<T> &v, ll N) { return Sum(v, 0, N - 1); }
template<class T> inline T Sum(vector<T> &v) { return Sum(v, v.size()); }
template<class T> inline T SumMOD(vector<T> &v, ll S, ll E){ T s=v[S]; REPS(i, S+1, E)s=(s+v[i])%MOD; return s; }
template<class T> inline T SumMOD(vector<T> &v, ll N) { return SumMOD(v, 0, N - 1); }
template<class T> inline T SumMOD(vector<T> &v) { return SumMOD(v, v.size()); }

inline ll AddMOD(ll a, ll b) { return (a + b) % MOD; }
inline ll SubMOD(ll a, ll b) { return (a - b + MOD) % MOD; }
inline ll MulMOD(ll a, ll b) { return (a * b) % MOD; }

inline ll in() { ll x; cin >> x; return x; }
inline double inD() { double x; cin >> x; return x; }
inline string inS() { string x; cin >> x; return std::move(x); }
template<class T=ll> inline vector<T> in_v(ll N){ vector<T> v(N); REP(i, N)cin>>v[i]; return move(v); }
inline void To0origin(vll &v) { EACH(e, v) e--; }


ll N, K;
vll A, F;
vll prod;
//vector<std::pair<ll, ll>> prodSorted(N);


ll m2k(ll m){
	ll sum = 0;
	REP(i,N){
		if (prod[i] <= m) continue;
		sum += (A[i] - m / F[i]);
	}
	return sum;
}


// 汎用的な二分探索のテンプレ
ll binary_search(ll left, ll right) {

	/* どんな二分探索でもここの書き方を変えずにできる！ */
	while (right - left > 1) {
		ll mid = left + (right - left) / 2;
		ll k = m2k(mid);
		if (k <= K) right = mid;
		else left = mid;
	}

	/* left は条件を満たさない最大の値、right は条件を満たす最小の値になっている */
	return right;
}


int main()
{
	cin >> N>>K;
	A = in_v(N);
	F = in_v(N);
	prod.resize(N);

	//Aを降順にソート
	std::sort(A.begin(), A.end(),
		[](ll &a, ll &b) {return a > b; }
	);
	//Fを昇順にソート
	std::sort(F.begin(), F.end());
	
	REP(i, N){
		prod[i] = A[i] * F[i];
	}

	ll maxProd = MaxE(prod);

	ll ans = binary_search(-1, maxProd+1);
	cout << ans << '\n';
}


Measured memory_bytes: 4992