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

ans = 1
min_ = X[k] - A[k]
for i in range(k - 1, -1, -1):
    if X[i] < min_:
        break
    ans += 1
    min_ = min(min_, X[i] - A[i])

max_ = X[k] + A[k]
for i in range(k + 1, n + 2):
    if X[i] > max_:
        break
    ans += 1
    max_ = max(max_, X[i] + A[i])

print(ans)