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]
K1=K
while K1-1>=0 and left<=r[K1-1]<=right:
  left=min(r[K1-1]-A[K1-1],left)
  right=max(r[K1-1]+A[K1-1],right)
  K1-=1
  low=K1
while K+1<=N-1 and r[K+1]<=right:
  right=max(r[K+1]+A[K+1],right)
  left=min(r[K+1]-A[K-1],left)
  K+=1
print(K-K1+1)