N,K = map(int,input().split())
X = list(map(int,input().split()))
A = list(map(int,input().split()))
kukan = [X[K-1]-A[K-1], X[K-1]+A[K-1]]
l = r = K-1
flg = True
while flg:
  flg = False
  while l >= 1 and kukan[0] <= X[l-1]:
    l-=1
    kukan[0] = min(kukan[0], X[l]-A[l])
    kukan[1] = max(kukan[1], X[l]+A[l])
    flg = True
  while r <= N-2 and X[r+1] <= kukan[1]:
    r+=1
    kukan[0] = min(kukan[0], X[r]-A[r])
    kukan[1] = max(kukan[1], X[r]+A[r])
    flg = True
print(r-l+1)