from math import *
n,h=list(map(int,input().split()))
w=list(map(int,input().split()))
l=list(map(int,input().split()))
maxi=0
for i in range(n):
    hei=ceil(max(0,(w[i]-l[i])+0.75*l[i]-h))
    if hei>maxi:
        maxi=hei
print(maxi)