#include "bits/stdc++.h"


using namespace  std;

int main(){
  int n;cin>>n;
  vector<int> v(n);
  for(int i=0;i<n;i++){
    cin>>v[i];
  }
sort(v.begin(),v.end());
  
cout<<v[n/2]-v[n/2-1]<<endl;

}