#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i,a,b) for(it i=(it)(a);i<=(it)b;i++)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define moda 998244353LL
#define modb 1000000007LL
#define dai 2500000000000000000LL
#define tyu 2500000000
#define sho -dai
#define eps 1e-14
#define yn(x) cout<<(x ? "Yes":"No")<<endl;
using it=long long;
using un=unsigned long long;
using db=long double;
using st=string;
using ch=char;
using bo=bool;
using P=pair<it,it>;
using T=tuple<it,it,it>;
using vi=vector<it>;
using vd=vector<db>;
using vs=vector<st>;
using vc=vector<ch>;
using vb=vector<bo>;
using vp=vector<P>;
using sp=set<P>;
using ss=set<st>;
using si=set<it>;
using vvi=vector<vi>;
using vvd=vector<vd>;
using vvs=vector<vs>;
using vvb=vector<vb>;
using vvc=vector<vc>;
using vvp=vector<vp>;
using vsi=vector<si>;
using vsp=vector<sp>;
using vvsi=vector<vsi>;
using vvsp=vector<vsp>;
using vvvi=vector<vvi>;
using vvvd=vector<vvd>;
using vvvvi=vector<vvvi>;
using mint=modint;
const it dx[4]={0,1,0,-1};
const it dy[4]={1,0,-1,0};

vi haba(vsi &g,it n,it s){
  vi dist(n,-1);
  dist[s]=0;
  queue<it> que;
  que.push(s);
  while(!que.empty()){
    it u=que.front();que.pop();
    for(it i:g[u]){
      if(dist[i]==-1){
        dist[i]=dist[u]+1;
        que.push(i);
      }
    }
  }
  return dist;
}

int main(){
  it n,k;cin>>n>>k;
  vi x(n),a(n);vsi g(n);
  rep(i,0,n-1)cin>>x[i];
  rep(i,0,n-1)cin>>a[i];
  rep(i,0,n-2){
    if(x[i+1]-x[i]<=a[i])g[i].insert(i+1);
    if(x[i+1]-x[i]<=a[i+1])g[i+1].insert(i);
  }
  vi t=haba(g,n,k-1);it b=0;
  rep(i,0,n-1)b+=(t[i]!=-1);
  cout<<b<<endl;
}