N,K=map(int,input().split())
r=list(map(int,input().split()))
A=list(map(int,input().split()))
K-=1
left=r[K]-A[K]
right=r[K]+A[K]
updated=True
K1=K
while updated:
  updated=False
  while K1-1>=0 and left<=r[K1-1]<=right:
    updated=True
    left=min(r[K1-1]-A[K1-1],left)
    right=max(r[K1-1]+A[K1-1],right)
    K1-=1
  while K+1<=N-1 and r[K+1]<=right:
    updated=True
    right=max(r[K+1]+A[K+1],right)
    left=min(r[K+1]-A[K+1],left)
    K+=1
print(K-K1+1)