N,K=map(int,input().split())
inf=float("inf")

X=list(map(int,input().split()))
X=[-inf]+X+[inf]

A=list(map(int,input().split()))
A=[0]+A+[0]

s,t=-1,-1

p=q=K
Left =X[K]-A[K]
Right=X[K]+A[K]

while (p,q)!=(s,t):
    s,t=p,q

    if Left<=X[p-1]:
        Left =min(Left ,X[p-1]-A[p-1])
        Right=max(Right,X[p-1]+A[p-1])
        p-=1

    if X[q+1]<=Right:
        Left =min(Left ,X[q+1]-A[q+1])
        Right=max(Right,X[q+1]+A[q+1])
        q+=1

print(q-p+1)