N,K = map(int,input().split())
frogs_p = [int(i) for i in input().split()]#蛙の位置
frogs_v = [int(i) for i in input().split()]#蛙の鳴き声の大きさ
cnt = 1
#K番目が鳴いた時、声が響く区間
section=[frogs_p[K-1]-frogs_v[K-1],frogs_p[K-1]+frogs_v[K-1]]
#Kより手前について
for i in range(1,K):
    if section[0] <= frogs_p[K-1-i]:#?in range とどちらが早いか
        section[0] = frogs_p[K-1-i] - frogs_v[K-1-i]
        cnt +=1
#Kより後について
for i in range(1,N-K):
    if section[1] >= frogs_p[K-1+i]:
        section[1] = frogs_p[K-1+i]+frogs_v[K-1+i]
        cnt +=1
print(cnt)