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

i = K-1
j = K-1
l = X[i]
r = X[j]
while True:
    flag = True
    l = min(l, X[i]-A[i], X[j]-A[j])
    r = max(r, X[i]+A[i], X[j]+A[j])
    if i > 0 and X[i-1] >= l:
        i -= 1
        flag = False
    if j < N-1 and X[j+1] <= r:
        j += 1
        flag = False
    if flag:
        break

print(j-i+1)