import bisect
n, k = map(int, input().split())
x = list(map(int, input().split()))
a = list(map(int, input().split()))

now = k-1
l = x[now] - a[now]
r = x[now] + a[now]
nowl = k-1
nowr = k-1
pl = 0
pr = 0
allfrog = 0


for i in range(n*10):
    bl = bisect.bisect_left(x, l)
    br = bisect.bisect_right(x, r) - 1
    for now in range(bl, nowl+1):
        l = min(l, x[now] - a[now])
        r = max(r, x[now] + a[now])
    for now in range(br, nowr+1):
        l = min(l, x[now] - a[now])
        r = max(r, x[now] + a[now])
    nowl = bl
    nowr = br
    pl = l
    pr = r

ans = 0
print(bisect.bisect_right(x, r) - bisect.bisect_left(x, l))