# 公式解説も同じ考え、区間を更新する、左端と右端
# 公式解説のやり方だと左も右も一歩ずつ進んでループがない
# 左端限界値、右端限界値を管理

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

left_idx = K
right_idx = K
left_min = X[K]-A[K]
right_max = X[K]+A[K]

while True:
    update = False
    while left_idx-1 >= 1 and left_min <= X[left_idx-1]:
        update = True
        left_idx -= 1
        left_min = min(left_min, X[left_idx]-A[left_idx])
        right_max = max(right_max, X[left_idx]+A[left_idx])
    while right_idx+1 <= N and right_max >= X[right_idx+1]:
        update = True
        right_idx += 1
        left_min = min(left_min, X[right_idx]-A[right_idx])
        right_max = max(right_max, X[right_idx]+A[right_idx])
    if update == False:
        break

ans = right_idx + 1 - left_idx
print(ans)