N,K=map(int, input().split())
X=list(map(int, input().split()))
A=list(map(int, input().split()))
import bisect
D=[]
for i in range(N):
  l=bisect.bisect_left(X,X[i]-A[i])
  r=bisect.bisect_right(X,X[i]+A[i])-1
  D.append((l,r))
#print(D)
from collections import deque
d=deque()
d.append(K-1)
E=[0]*N
E[K-1]=1
ll,rr=K-1,K-1
while d:
  now=d.popleft()
  l,r=D[now]
  if 0<ll:
    if l<ll:
      for i in range(l,ll):
        if E[i]==1:
          break
        else:
          E[i]=1
          d.append(i)
  if rr<N-1:
    if rr<r:
      for i in range(r,rr,-1):
        if E[i]==1:
          break
        else:
          E[i]=1
          d.append(i)
print(sum(E))