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

K -= 1
right = K + 1
left = K - 1
stack = [K]
ans = 0
while stack:
    now = stack.pop()
    ans += 1
    r = X[now] + A[now]
    l = X[now] - A[now]
    while right < N and X[right] <= r:
        stack.append(right)
        right += 1
    while left >= 0 and X[left] >= l:
        stack.append(left)
        left -= 1
print(ans)