from collections import deque
import bisect

n,k = map(int,input().split())
x = [int(i) for i in input().split()]
a = [int(i) for i in input().split()]

ans = [0]*(n)

d = deque()
d.append(k-1)
l = k-1
r = k-1
ans[k-1] = 1

while len(d):
    tmp = d.popleft()
    pos = x[tmp]
    nl = bisect.bisect_left(x,pos-a[tmp])
    nr = bisect.bisect_right(x,pos+a[tmp])
    for i in range(nl,l):
        #if ans[i] == 1:
        #    break
        d.append(i)
        ans[i] = 1
    for i in range(nr-1,r-1,-1):
        #if ans[i] == 1:
        #    break
        d.append(i)
        ans[i] = 1
    l = min(l,nl)
    r = max(r,nr)
print(sum(ans))