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

K-=1
ANS=[0]*N
PLUS=X[K]+A[K]
MINUS=X[K]-A[K]

for roop in range(100):

    for i in range(N):
        if X[i]<=PLUS and X[i]>=MINUS:
            ANS[i]=1
            PLUS=max(PLUS,X[i]+A[i])
            MINUS=min(MINUS,X[i]-A[i])

    for i in range(N-1,-1,-1):
        if X[i]<=PLUS and X[i]>=MINUS:
            ANS[i]=1
            PLUS=max(PLUS,X[i]+A[i])
            MINUS=min(MINUS,X[i]-A[i])

print(sum(ANS))