from collections import deque
from bisect import bisect_left, bisect_right

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

ans = 0
q = deque()
q.append(K)
l = r = K
while len(q):
    k = q.popleft()
    ans += 1
    _l = bisect_left(X, X[k] - A[k])
    for i in range(_l, l):
        q.append(i)
    l = min(l, _l)

    _r = bisect_right(X, X[k] + A[k]) - 1
    for i in range(r+1, _r + 1):
        q.append(i)
    r = max(r, _r)

print(ans)