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