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

K-=1
ANS=1
PLUS=X[K]+A[K]
MINUS=X[K]-A[K]

for i in range(K+1,N):
    if X[i]<=PLUS:
        ANS+=1
        PLUS=max(PLUS,X[i]+A[i])

for i in range(K-1,-1,-1):
    if X[i]>=MINUS:
        ANS+=1
        MINUS=min(MINUS,X[i]-A[i])

print(ANS)