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]
LF=1
RF=1
l=0
r=0
def Left(a):
    global R
    global L
    global LF
    global RF
    global l
    global r
    for i in range(a,10**5+5):
        if L<=P[K-i]:
            if L>P[K-i]-A[K-i]:
                L=P[K-i]-A[K-i]
            if R<P[K-i]+A[K-i]:
                R=P[K-i]+A[K-i]
                RF=1
        else:
            l=i
            LF=0
            break
#print(i)
def Right(a):
    global R
    global L
    global RF
    global LF
    global l
    global r
    for j in range(a,10**5+5):
        if R>=P[K+j]:
            if R<P[K+j]+A[K+j]:
                R=P[K+j]+A[K+j]
            if L>P[K+j]-A[K+j]:
                L=P[K+j]-A[K+j]
                LF=1
        else:
            RF=0
            r=j
            break

for k in range(10**5+5):
    if RF==1:
        Right(r)
    elif LF==1:
        Left(l)
    else:
        break
    

#print(j)
print(max(l+r-1,1))