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

q = deque()
q.append(K)
lk = rk = K
l = r = X[K]
while len(q):
    k = q.popleft()
    _l = X[k] - A[k]
    _r = X[k] + A[k]

    if _l < l:
        _lk = bisect_left(X, _l)
        if _lk < lk:
            for i in range(lk-1, _lk-1, -1):
                q.append(i)
            lk = _lk
        l = _l

    if _r > r:
        _rk = bisect_right(X, _r)
        if _rk > rk:
            for i in range(rk+1, _rk):
                q.append(i)
            rk = _rk
        r = _r

print(rk - lk or 1)