N,K=map(int,input().split())
P=list(map(int,input().split()))
INF=float('inf')
P=[-INF]+P+[INF]
A=list(map(int,input().split()))
A=[0]+A+[0]


L=P[K]-A[K]
R=P[K]+A[K]

for i in range(10**5+5):
    if L<=P[K-i]:
        if L>P[K-i]-A[K-i]:
            L=P[K-i]-A[K-i]
    else:
        break
#print(i)

for j in range(10**5+5):
    if R>=P[K+j]:
        if R<P[K+j]+A[K+j]:
            R=P[K+j]+A[K+j]
    else:
        break
#print(j)
print(max(i+j-1,1))