#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 now=K;
  while(x[now]-x[now-1]<=a[now])now--;
  int left=now;
  now=K;
  while(x[now+1]-x[now]<=a[now])now++;
  cout<<now-left+1<<endl;
}