Problem:
Score : 300 points

Problem Statement

Takahashi made N problems for competitive programming.
The problems are numbered 1 to N, and the difficulty of Problem i is represented as an integer d_i (the higher, the harder).

He is dividing the problems into two categories by choosing an integer K, as follows:

A problem with difficulty K or higher will be for ARCs.

A problem with difficulty lower than K will be for ABCs.

How many choices of the integer K make the number of problems for ARCs and the number of problems for ABCs the same?

Problem Statement

2 \leq N \leq 10^5

N is an even number.

1 \leq d_i \leq 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
d_1 d_2 ... d_N

Output

Print the number of choices of the integer K that make the number of problems for ARCs and the number of problems for ABCs the same.

Sample Input 1

6
9 1 4 4 6 7

Sample Output 1

2

If we choose K=5 or 6, Problem 1, 5, and 6 will be for ARCs, Problem 2, 3, and 4 will be for ABCs, and the objective is achieved.
Thus, the answer is 2.

Sample Input 2

8
9 1 14 5 5 4 4 14

Sample Output 2

0

There may be no choice of the integer K that make the number of problems for ARCs and the number of problems for ABCs the same.

Sample Input 3

14
99592 10342 29105 78532 83018 11639 92015 77204 30914 21912 34519 80835 100000 1

Sample Output 3

42685

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

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

using ll = long long;
using ull = unsigned long long;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i < (n); i++)
#define all(a) begin(a),end(a)
template<class T> inline void sort_uniq(T& c) { sort(ALL(c)); c.erase(unique(ALL(c)), c.end()); }
template<class T> istream& operator >> (istream& s, vector<T>& v)
{ for (T& x: v) { s >> x; } return s;}
template<class T> void cout_v(const vector<T>& c)
{ for (int i = 0; i < c.size(); i++) cout << c[i] << endl; }
template<class K, class V> void cout_v(map<K, V>& m)
{ for(auto it=m.begin();it!=m.end();it++)cout<<it->first<<":"<<it->second<<endl;}
template<class T> void cout_h(const vector<T>& c)
{ for (int i = 0; i < c.size(); i++) cout << c[i] << (i==c.size()-1?"\n":" "); }
template<class T> inline bool chmin(T& a, T b) {return a>b?a=b,true:false;}
template<class T> inline bool chmax(T& a, T b) {return a<b?a=b,true:false;}
inline int powi(int x,int y) {int p=1; while(y--) p*=x; return p;}
inline ll powll(ll x,ll y) {ll p=1; while(y--) p*=x; return p;}
template<class T> inline bool is_overlap(const T& a, const T& b, const T& p, const T& q)
{ return p <=b && a <= q; }
#define MOD = 1000000007;
#define SP << " " <<
#define FMT(a) #a<<":"<<a 
#define FMT2(a,b) #a<<":"<<a<<", "<<#b<<":"<<b 
#define FMT3(a,b,c) #a<<":"<<a<<", "<<#b<<":"<<b<<", "<<#c<<":"<<c 
#define FMT4(a,b,c,d) #a<<":"<<a<<", "<<#b<<":"<<b<<", "<<#c<<":"<<c<<", "<<#d<<":"<<d 
void yes(bool f){cout<<(f?"yes":"no")<<endl;}
void Yes(bool f){cout<<(f?"Yes":"No")<<endl;}
void YES(bool f){cout<<(f?"YES":"NO")<<endl;}

int main()
{
    cin.tie(0); ios::sync_with_stdio(false);
    //cout<<std::fixed<<std::setprecision(10);

    int N; cin >>N;
    vector<int> d(N); cin >> d;
    sort(all(d));
    cout << d[N/2] - d[N/2-1] << endl;
}