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

ans = 0

now = X[K-1] + A[K-1]
for i in range(K,N):
    if X[i] <= now:
        ans += 1
        if X[i] + A[i] > now:
            now = X[i] + A[i]
now = X[K-1] - A[K-1]
for i in reversed(range(K-1)):
    if X[i] >= now:
        ans += 1
        if X[i] - A[i] < now:
            now = X[i] - A[i]
print(ans + 1)