#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int n,k;
  cin>>n>>k;
  vector<Int> xs(n),as(n);
  for(Int i=0;i<n;i++) cin>>xs[i];
  for(Int i=0;i<n;i++) cin>>as[i];

  k--;
  Int l=k,r=k;
  vector<Int> used(n,0);
  queue<Int> que;
  used[k]=1;
  que.emplace(k);

  Int p=k,q=k;
  while(!que.empty()){
    Int v=que.front();que.pop();
    {
      Int w=--upper_bound(xs.begin(),xs.end(),xs[v]+as[v])-xs.begin();
      chmax(r,w);
    }
    {
      Int w=lower_bound(xs.begin(),xs.end(),xs[v]-as[v])-xs.begin();
      chmin(l,w);
    }
    //cout<<v<<":"<<l<<" "<<r<<endl;
    while(p-1>=l && !used[p-1]){
      p--;
      used[p]=1;
      que.emplace(p);
    }
    while(q+1<=r && !used[q+1]){
      q++;
      used[q]=1;
      que.emplace(q);
    }
  }

  Int ans=r-l+1;
  cout<<ans<<endl;
  return 0;
}