from bisect import *

N, K = map(int, input().split())
X = list(map(int, input().split()))
A = list(map(int, input().split()))
K -= 1
i = K

for _ in range(N):
    m = bisect_right(X, X[i]+A[i])
    i = m - 1

r = i
i = K

for _ in range(N):
    m = bisect_left(X, X[i]-A[i])
    i = m

l = i

print(r - l + 1)