/*
	By: harshvcode | harshvsingh.223@gmail.com
	Created at: 03:46:09_PM_21-JUNE-2020
*/
#include <bits/stdc++.h>
#define LL long long
#define M 1000000009
#define NL '\n';
#define PB push_back
#define Ai vector<int> arr
using namespace std;
int main()
{
	ios::sync_with_stdio(0);
  	cin.tie(0);
	int n,h;
	cin >> n >> h;
	int ans=0;
	Ai(n),len(n);
	for(int i=0; i<n ;i++) cin >> arr[i];
	for(int i=0; i<n; i++) cin >> len[i];
	for(int i=0; i<n; i++){
		int checker=arr[i] - h;
		if(checker < 1) continue;
		ans=max(ans,(checker - (len[i] / 4)));
	}
	cout << ans << NL;
	return 0;
}