/* -*- coding: utf-8 -*-
 *
 * 871.cc:  No.871 かえるのうた - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

typedef long long ll;
typedef queue<int> qi;

/* global variables */

ll xs[MAX_N], as[MAX_N];
bool used[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  k--;

  for (int i = 0; i < n; i++) scanf("%lld", xs + i);
  for (int i = 0; i < n; i++) scanf("%lld", as + i);

  int li = k, ri = k + 1;
  used[k] = true;
  qi q;
  q.push(k);

  while (! q.empty()) {
    int u = q.front(); q.pop();
    int uli = lower_bound(xs, xs + n, xs[u] - as[u]) - xs;
    int uri = upper_bound(xs, xs + n, xs[u] + as[u]) - xs;
    
    while (uli < li) {
      --li;
      used[li] = true;
      q.push(li);
    }

    while (ri < uri) {
      used[ri] = true;
      q.push(ri);
      ri++;
    }
  }
  //printf("li=%d, ri=%d\n", li, ri);

  printf("%d\n", ri - li);
  return 0;
}