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
while l > 0:
    if X[l-1] >= X[l]-A[l]:
        l -= 1
    else:
        break

r = K-1
while r < N-1:
    if X[r+1] <= X[r]+A[r]:
        r += 1
    else:
        break

print(r-l+1)