#include<bits/stdc++.h>
using namespace std;

#define rep(i,n) for(ll i=0;i<(n);++i)
using ll = long long;
using pll = pair<ll,ll>;
constexpr ll INF = (1LL<<60);
constexpr ll MOD = (1e9+7);
//constexpr ll MOD = (998244353);
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}return 0;}
void dump(){cout<<endl;}
template<class T,class... Ts> void dump(T&& h, Ts&&... t){cout<<h<<", ";dump(forward<Ts>(t)...);}
template<class T> istream &operator>>(istream&is,vector<T>&v){for(auto &elemnt:v)is>>elemnt;return is;}
template<class T,class U> istream &operator>>(istream&is,pair<T,U>&p){is>>p.first>>p.second;return is;}
template<class T>vector<T> make_vector(size_t a){return vector<T>(a);}
template<class T, class... Ts>auto make_vector(size_t a, Ts... ts){return vector<decltype(make_vector<T>(ts...))>(a, make_vector<T>(ts...));}

void solve1();void solve2();
int main(){
  solve1();
  return 0;
}

void solve1(){

  ll n,k;
  cin>>n>>k;
  k--;
  vector<ll> x(n),a(n);
  cin>>x>>a;

  ll ans = 1;
  for(ll i=k;i+1<n;++i){
    if(a[i]+x[i]>=x[i+1])ans++;
    else break;
  }
  for(ll i=k;i>0;--i){
    if(x[i]-a[i]<=x[i-1])ans++;
    else break;
  }

  cout<<(ans)<<endl;

}