//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,abm,mmx,avx,avx2,popcnt,tune=native")
//#pragma GCC optimize("SEX_ON_THE_BEACH")	
//#pragma GCC optimize("fast-math")
//#pragma GCC optimize("unroll-loops")
//#pragma comment(linker, "/STACK:36777216")

#define _CRT_SECURE_NO_WARNINGS
#include <chrono>
#include <set>
#include <map>
#include <deque>
#include <cmath>
#include <queue>
#include <cassert>
#include <random>
#include <bitset>
#include <iomanip>
#include <numeric>
#include <time.h>//////////////
#include <ctime>
#include <string>
#include <cstdio>
#include <vector>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
#define endl '\n'
#define mp make_pair
#define pbc push_back
#define pob pop_back()
#define empb emplace_back
#define queuel queue<long long>
#define sqr(a) ((a) * (a))
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pin(p) cin >> p.first >> p.second;
#define uniq(a) sort(all(a));(a).resize(unique(all(a)) - a.begin());
#define rev(v) reverse(v.begin(), v.end());
#define sout(s, c) for (auto i : s) cout << i << c;
#define pout(p) cout << p.first << " " << p.second;
#define er(v, l, r) erase(v.begin() + l, v.begin() + r);
#define vin(v) for (ll i = 0; i < v.size(); ++i) cin >> v[i];
#define vout(v, c) for (int i = 0; i < v.size(); ++i) cout << v[i] << c;
#define pushi(v, a) for (int i = 0; i < a.size(); ++i) v.push_back(a[i]);
#define fastio() ios_base::sync_with_stdio(0); cout.tie(0); cin.tie(0); srand(time(NULL))
#define sp system("pause")
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
using namespace std;
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
const ld EPS = 1e-5;
const ld PI = acos(-1.0);
int mod = (int)998244353;
const int MOD7 = 1000000007;
const int MOD9 = 1000000009;
const int a228 = 18;
const ll kekmod = 1791791791;
const ll bestmod = 1148822869;
vector<ll> mods = { kekmod,bestmod,mod,MOD9,1000000007 };
vector<ll> hashpows = { 29,31,37,43,47,53,179,229 };
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count() + 228 + 'i' + 'q' + 1337 + 1488);
ll MOD = mods[rnd() % mods.size()];
ll hashpow = hashpows[rand() % hashpows.size()];
#define int ll
int n, k;
bool  check(vector<int> &a, vector<int> &b, int t)
{
	int tans = 0;
	for (int i = 0; i < n; ++i)
	{
		int tx = a[i] * b[i];
		if (tx <= t) continue;
		int dd = tx - t;
		tans += (dd + b[i] - 1) / b[i];
	}
	return tans <= k;
}
signed main()
{
	fastio();
	cin >> n >> k;
	vector<int> a(n);
	vector<int> b(n);
	vin(a);
	vin(b);
	sort(all(b));
	sort(rall(a));
	int l = -1, r = 1e18;
	while (r - l > 1)
	{
		int m = (l + r) / 2;
		if (check(a, b, m)) r = m;
		else l = m;
	}
	cout << r;
//	sp;
}


Measured memory_bytes: 3456