N,K=map(int,input().split())
inf=float("inf")

X=list(map(int,input().split()))
X=[-inf]+X+[inf]

A=list(map(int,input().split()))
A=[0]+A+[0]


p=q=K
while X[p]-A[p]<=X[p-1]:
    p-=1

while X[q+1]<=X[q]+A[q]:
    q+=1

print(q-p+1)