//ええなにそれ・・・割り算ってllよりdoubleの方が速いとでも？
#pragma GCC optimize ("O3")
#pragma GCC target ("avx")
#include<bits/stdc++.h>
#include<cstdio>
#include<algorithm>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define Would
#define you
#define please

const int cm = 1 << 17;
char cn[cm], * ci = cn + cm, ct;
inline char getcha() {
	if (ci - cn == cm) { fread_unlocked(cn, 1, cm, stdin); ci = cn; }
	return *ci++;
}
inline int getint() {
	int A = 0;
	if (ci - cn + 16 > cm) while ((ct = getcha()) >= '0') A = A * 10 + ct - '0';
	else while ((ct = *ci++) >= '0') A = A * 10 + ct - '0';
	return A;
}
inline ll getll() {
	ll A = 0;
	if (ci - cn + 24 > cm) while ((ct = getcha()) >= '0') A = A * 10 + ct - '0';
	else while ((ct = *ci++) >= '0') A = A * 10 + ct - '0';
	return A;
}

ll tmp[200001];
void pakuri_sort(int N, int A[]) {
	const int b = 10;
	rep(k, 2) {
		int kazu[1 << b] = {}, kazu2[1 << b] = {};
		rep(i, N) kazu[A[i] >> k * b & ((1 << b) - 1)]++;
		rep(i, (1 << b) - 1) kazu[i + 1] += kazu[i];
		for (int i = N - 1; i >= 0; i--) tmp[--kazu[A[i] >> k * b & ((1 << b) - 1)]] = A[i];
		k++;
		rep(i, N) kazu2[tmp[i] >> k * b & ((1 << b) - 1)]++;
		rep(i, (1 << b) - 1) kazu2[i + 1] += kazu2[i];
		for (int i = N - 1; i >= 0; i--) A[--kazu2[tmp[i] >> k * b & ((1 << b) - 1)]] = tmp[i];
	}
}
void pakuri_sort2(int N, int A[]) {
	const int b = 10;
	rep(k, 2) {
		int kazu[1 << b] = {}, kazu2[1 << b] = {};
		rep(i, N) kazu[A[i] >> k * b & ((1 << b) - 1)]++;
		for (int i = (1 << b) - 2; i >= 0; i--) kazu[i] += kazu[i + 1];
		for (int i = N - 1; i >= 0; i--) tmp[--kazu[A[i] >> k * b & ((1 << b) - 1)]] = A[i];
		k++;
		rep(i, N) kazu2[tmp[i] >> k * b & ((1 << b) - 1)]++;
		for (int i = (1 << b) - 2; i >= 0; i--) kazu2[i] += kazu2[i + 1];
		for (int i = N - 1; i >= 0; i--) A[--kazu2[tmp[i] >> k * b & ((1 << b) - 1)]] = tmp[i];
	}
}
ll AF[200000];
void pakuri_sort3(int N, ll A[]) {
	const int b = 10;
	for (int k = 2; k < 6; k++) {
		int kazu[1 << b] = {}, kazu2[1 << b] = {};
		rep(i, N) kazu[A[i] >> k * b & ((1 << b) - 1)]++;
		rep(i, (1 << b) - 1) kazu[i + 1] += kazu[i];
		for (int i = N - 1; i >= 0; i--) tmp[--kazu[A[i] >> k * b & ((1 << b) - 1)]] = A[i];
		k++;
		rep(i, N) kazu2[tmp[i] >> k * b & ((1 << b) - 1)]++;
		rep(i, (1 << b) - 1) kazu2[i + 1] += kazu2[i];
		for (int i = N - 1; i >= 0; i--) A[--kazu2[tmp[i] >> k * b & ((1 << b) - 1)]] = tmp[i];
	}
}

int main() {
	//cin.tie(0);
	//ios::sync_with_stdio(false);


	ll N = getint(), K = getll();
	int A[200000], F[200000];
	rep(i, N) A[i] = getint();
	rep(i, N) F[i] = getint();
	pakuri_sort(N, A);
	pakuri_sort2(N, F);
	rep(i, N) AF[i] = ((ll)A[i] * F[i] << 20) + F[i];
	const int m = (1 << 20) - 1;
	pakuri_sort3(N, AF);

	ll L = -1, R = 1e12;
	while (L + 1 < R) {
		ll M = (L + R) / 2;
		ll kazu = 0;
		for (auto itr = lower_bound(AF, AF + N, M << 20); itr != AF + N; itr++) {
			kazu += ceil((double)((*itr >> 20) - M) / (*itr & m));
			if (kazu > K) break;
		}
		if (kazu > K) L = M;
		else R = M;
	}

	printf("%lld", R);


	Would you please return 0;
}

Measured memory_bytes: 5120