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

l,r=K-1,K-1
L,R=X[l]-A[l],X[r]+A[r]
while (r+1<N and X[r+1]<=R) or (l>0 and X[l-1]>=L):
    if r+1<N and X[r+1]<=R:
        r+=1
        R=max(X[r]+A[r],R)
        L=min(X[r]-A[r],L)
    if l>0 and X[l-1]>=L:
        l-=1
        R=max(X[l]+A[l],R)
        L=min(X[l]-A[l],L)
print(r-l+1)