#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	int arr[n];
	for(int i=0;i<n;i++)
	{
		cin>>arr[i];
	}
	sort(arr,arr+n);
	int p=arr[n/2];
	int q=arr[n/2-1];
	if(p==q)
		cout<<0<<endl;
	else cout<<p-q<<endl;
}
