N, K = map(int, input().split())
X = [0] + list(map(int, input().split()))
A = [0] + list(map(int, input().split()))

L = R = K
Ld, Rd = X[K] - A[K], X[K] + A[K]

flag = True
while flag:
    flag = False
    while L - 1 >= 1 and Ld <= X[L - 1]:
        flag = True
        L -= 1
        Ld = min(Ld, X[L] - A[L])
        Rd = max(Rd, X[L] + A[L])
    while R + 1 <= N and Rd >= X[R + 1]:
        flag = True
        R += 1
        Rd = max(Rd, X[R] + A[R])
        Ld = min(Ld, X[R] - A[R])
print(R - L + 1)