import sys
input = sys.stdin.readline

from bisect import *
from collections import deque

class UnionFind:
    def __init__(self, num):
        self.rank = [0] * num
        self.par = [i for i in range(num)]
        self.n = num
 
    def find_root(self, node):
        if self.par[node] == node:
            return node
        else:
            self.par[node] = self.find_root(self.par[node])
            return self.par[node]
 
    def same_root(self, x, y):
        return self.find_root(x) == self.find_root(y)
 
    def union(self, x, y):
        x = self.find_root(x)
        y = self.find_root(y)
        if x == y:
            return
        if self.rank[x] > self.rank[y]:
            self.par[y] = x
        else:
            self.par[x] = y
            if self.rank[x] == self.rank[y]:
                self.rank[y] += 1

N,K = map(int,input().split())
X = list(map(int,input().split()))
A = list(map(int,input().split()))

UF = UnionFind(N)
q = deque([K-1])

ok = [False]*N
ok[K-1] = True

while q :
    indn = q.popleft()
    x = X[indn]
    indl = bisect_left(X,x-A[indn])
    for j in range(indl,indn) :
        if ok[j] :
            continue
        ok[j] = True
        q.append(j)
    indr = bisect_right(X,x+A[indn])-1
    for j in range(indn+1,indr+1) :
        if ok[j] :
            continue
        ok[j] = True
        q.append(j)
print(ok.count(True))