from bisect import bisect_left, bisect_right
N, K = map(int, input().split())
X = list(map(int, input().split())) + [10 ** 18]
A = list(map(int, input().split())) + [0]


visited = [0] * N
stack = [K - 1]

while stack:
    fr = stack.pop()
    visited[fr] = 1

    l = bisect_left(X, X[fr] - A[fr])
    r = bisect_right(X, X[fr] + A[fr])

    for to in range(l, fr):
        if visited[to]:
            continue
        stack.append(to)

    for to in range(fr + 1, r):
        if visited[to]:
            continue
        stack.append(to)

print(sum(visited))