import sys
input=lambda: sys.stdin.readline().rstrip()
n,k=map(int,input().split())
X=[int(i) for i in input().split()]
A=[int(i) for i in input().split()]
l,r=X[k-1]-A[k-1],X[k-1]+A[k-1]
ll,rr=k-1,k-1
while True:
  if ll-1>=0 and X[ll-1]>=l:
    l=min(l,X[ll-1]-A[ll-1])
    r=max(r,X[ll-1]+A[ll-1])
    ll-=1
  elif rr+1<n and X[rr+1]<=r:
    r=max(r,X[rr+1]+A[rr+1])
    l=min(l,X[rr+1]-A[rr+1])
    rr+=1 
  else:
    break
print(rr-ll+1)