N,K = map(int, input().split())
X = [int(x) for x in input().split()]
A = [int(a) for a in input().split()]

l = K-1
p = A[l]
while l > 0:
    p = min(p, X[l]-A[l])
    if X[l-1] >= p:
        l -= 1
    else:
        break

r = K-1
p = A[r]
while r < N-1:
    p = max(p, X[r]+A[r])
    if X[r+1] <= p:
        r += 1
    else:
        break

print(r-l+1)