N,K=map(int, input().split())
A=list(map(int, input().split()))
B=list(map(int, input().split()))
if N==1:
  print(1)
  exit()
ans=1
r=K-1
while r<N-1:
  d=A[r+1]-A[r]
  if d<=B[r]:
    ans+=1
    r+=1
  else:
    break
l=K-1
while 0<l:
  d=A[l]-A[l-1]
  if d<=B[l]:
    ans+=1
    l-=1
  else:
    break
print(ans)