#include <bits/stdc++.h>
using namespace std;
const int MOD=1e9+7;
const int INF=1e9;
//const int MOD=998244353;
const long long LINF=1e18;
#define int long long
//template
//main
signed main(){
  int N,K;cin>>N>>K;
  std::vector<int> x(N+2),a(N+2);
  for(int i=0;i<N;i++)cin>>x[i+1];
  for(int i=0;i<N;i++)cin>>a[i+1];
  x[0]=-LINF;x[N+1]=LINF;a[0]=a[N+1]=0;
  int rnow=K,lnow=K;//声を出した右端と左端
  int left=x[K]-a[K],right=x[K]+a[K];
  bool f=true;
  while(f){
    f=false;
    if(x[rnow+1]<=right){
      rnow++;
      right=max(right,x[rnow]+a[rnow]);
      left=min(left,x[rnow]-a[rnow]);
      f=true;
    }
    if(x[lnow-1]>=left){
      lnow--;
      right=max(right,x[lnow]+a[lnow]);
      left=min(left,x[lnow]-a[lnow]);
      f=true;
    }
  }
  cout<<rnow-lnow+1<<endl;
}