N,K = map(int,input().split())
X = list(map(int,input().split()))
A = list(map(int,input().split()))
K -= 1

migi = X[K] + A[K]
hidari = X[K] - A[K]
stack = [(K,1),(K,-1)]
ans = 1
while stack:
    now,d = stack.pop()
    if 0 <= now + d < N and hidari <= X[now + d] <= migi:
        migi = max(migi,X[now + d] + A[now + d])
        hidari = min(hidari,X[now + d] - A[now + d])
        stack.append((now + d,d))
        ans += 1
print(ans)