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]

for i in range(n):
    bl = bisect.bisect_left(x, l)
    br = bisect.bisect_right(x, r) - 1
    l = min(l, x[bl] - a[bl])
    r = max(r, x[br] + a[br])

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