n, k = map(int, input().split())
X = [-10 ** 20] + list(map(int, input().split())) + [10 ** 20]
A = [0] + list(map(int, input().split())) + [0]

flg = True
min_ = X[k] - A[k]
max_ = X[k] + A[k]
l = k - 1
r = k + 1
while flg:
    flg = False
    while X[l] >= min_:
        min_ = min(min_, X[l] - A[l])
        max_ = max(max_, X[l] + A[l])
        l -= 1
        flg = True
    while X[r] <= max_:
        min_ = min(min_, X[r] - A[r])
        max_ = max(max_, X[r] + A[r])
        r += 1
        flg = True
print(r - l - 1)