#include <iostream>
#include <queue>
using namespace std;
int main(){
  long long n,k;cin>>n>>k;
  
  vector<long long> X(n),A(n);
  for(int i = 0; n > i; i++)cin>>X[i];
  for(int i = 0; n > i; i++)cin>>A[i];
  vector<bool> G(n);
  queue<int> b;
  b.push(k-1);
  int nwl = k-1,nwr = k-1;
  while(b.size()){
    auto z = b.front();b.pop();
    while(nwr+1 != n && X[nwr+1]-X[z] <= A[z]){
        nwr++;
        b.push(nwr);
    }
    while(nwl-1 >= 0 && X[z]-X[nwl-1] <= A[z]){
        nwl--;
        b.push(nwl);
    }
  }
  cout << nwr-nwl+1 << endl;
}