N, K = map(int, input().split())
inf = float("inf")
X = [-inf] + list(map(int, input().split())) + [inf]
A = [-1] + list(map(int, input().split())) + [inf]

ans = [0] * (N + 2)

# left
L = X[K]
i = K
while i > 0:
    if X[i] >= L:
        ans[i] = 1
        L = min(L, X[i] - A[i])
        i -= 1
    else:
        break

# right
R = X[K]
i = K
while i < N + 1:
    if X[i] <= R:
        ans[i] = 1
        R = max(R, X[i] + A[i])
        i += 1
    else:
        break

print(sum(ans))