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]


p=K
Left=X[K]-A[K]

while Left<=X[p-1]:
    Left=min(Left,X[p-1]-A[p-1])
    p-=1

q=K
Right=X[K]+A[K]
while X[q+1]<=Right:
    Right=max(Right,X[q+1]+A[q+1])
    q+=1

print(q-p+1)