N,K = map(int,input().split())
X = list(map(int,input().split()))
A = list(map(int,input().split()))
migi = K
K -= 1
now = X[K] + A[K]
while migi < N and X[migi] <= now:
    now = max(now,X[migi] + A[migi])
    migi += 1
hidari = K
now = X[K] - A[K]
while hidari >= 0 and X[hidari] >= now:
    now = min(now,X[hidari] - A[hidari])
    hidari -= 1
print(migi - hidari - 1)