from bisect import *

N,K = map(int,input().split())
X = list(map(int,input().split()))
A = list(map(int,input().split()))

ans = 1
k = K-1

while True :
    if k == N-1 :
        break
    
    val = X[k] + A[k]
    ind = bisect_right(X,val)-1
    if k == ind :
        break
    else :
        ans += ind-k
        k = ind
k = K-1
while True :
    if k == 0 :
        break
    
    val = X[k] - A[k]
    ind = bisect_left(X,val)
    if k == ind :
        break
    else :
        ans += -(ind-k)
        k = ind
print(ans)