import sys, math
sys.setrecursionlimit(10**8)
sys.set_int_max_str_digits(0)
INF = 10**18
MOD = 998244353
from bisect import bisect_left, bisect_right
from collections import deque, defaultdict, Counter
from itertools import product, combinations, permutations, groupby, accumulate
from heapq import heapify, heappop, heappush
def I():   return sys.stdin.readline().rstrip()
def II():  return int(sys.stdin.readline().rstrip())
def IS():  return sys.stdin.readline().rstrip().split()
def MII(): return map(int, sys.stdin.readline().rstrip().split())
def LI():  return list(sys.stdin.readline().rstrip())
def TII(): return tuple(map(int, sys.stdin.readline().rstrip().split()))
def LII(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LSI(): return list(map(str, sys.stdin.readline().rstrip().split()))
def GMI(): return list(map(lambda x: int(x) - 1, sys.stdin.readline().rstrip().split()))
def kiriage(a, b): return (a+b-1)//b

N, K = MII()
X = LII()
A = LII()

done = [False] * N
que = deque()
que.append(K - 1)
done[K - 1] = True

while que:
    idx = que.popleft()
    pos = X[idx]
    # 座標が pos - A[idx] 以上の最小の点はどこか？
    cur = bisect_left(X, pos - A[idx])
    # left から右に向かって、done が True になるまでチェックする
    while True:
        if done[cur]:
            break
        done[cur] = True
        que.append(cur)
        cur += 1
    
    # 座標が pos + A[idx] 以下の最大の点はどこか？
    cur = bisect_right(X, pos + A[idx]) - 1
    while True:
        if done[cur]:
            break
        done[cur] = True
        que.append(cur)
        cur -= 1

ans = done.count(True)
print(ans)