from bisect import bisect, bisect_left
def inpl(): return list(map(int, input().split()))

N, K = inpl()
K -= 1
X= inpl()
A = inpl()

l = K
r = K
cl = K + 1
cr = K - 1

while cl > l and cr < r:
    for x in range(cl-1, l-1, -1):
        cl -= 1
        nr = bisect(X, X[x] + A[x]) - 1
        r = min(max(r, nr), N-1)
        nl = bisect_left(X, X[x] - A[x])
        l = max(min(l, nl), 0)
    
    for x in range(cr+1, r+1):
        cr += 1
        nr = bisect(X, X[x] + A[x]) - 1
        r = min(max(r, nr), N-1)
        nl = bisect_left(X, X[x] - A[x])
        l = max(min(l, nl), 0)

print(r-l+1)