#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

int main(){
  int n, k;
  cin >> n >> k;
  k--;
  vector<ll> x(n), a(n);
  rep(i,n) cin >> x[i];
  rep(i,n) cin >> a[i];
  
  queue<int> que;
  que.push(k);
  int minl = k, maxr = k;

  while (!que.empty()){
    int i = que.front(); que.pop();
    
    int l = lower_bound(x.begin(), x.end(), x[i] - a[i]) - x.begin();
    int r = upper_bound(x.begin(), x.end(), x[i] + a[i]) - x.begin();
    r--;
    while (l < minl){
      minl--;
      que.push(minl);
    }
    while (maxr < r){
      maxr++;
      que.push(maxr);
    }
    //cout << l << " " << r << endl;
  }
  cout << maxr - minl + 1 << endl;
  return 0;
}