from bisect import bisect_left, bisect_right
from collections import deque

n, k = map(int, input().split())
k -= 1
X = list(map(int, input().split()))
A = list(map(int, input().split()))

Que = deque([k])
seen = set([k])
left, right = k, k
while Que:
    idx = Que.popleft()
    l, r = X[idx] - A[idx], X[idx] + A[idx]
    lidx = bisect_left(X, l)
    ridx = bisect_right(X, r) - 1
    if lidx < left:
        for i in range(lidx, left):
            if i in seen:
                continue
            seen.add(i)
            Que.append(i)
        left = lidx
    if ridx > right:
        for i in range(right + 1, ridx + 1):
            if i in seen:
                continue
            seen.add(i)
            Que.append(i)
        right = ridx
print(right - left + 1)