Problem:
Score: 200 points

Problem Statement

We have N cards. A number a_i is written on the i-th card.

Alice and Bob will play a game using these cards. In this game, Alice and Bob alternately take one card. Alice goes first.

The game ends when all the cards are taken by the two players, and the score of each player is the sum of the numbers written on the cards he/she has taken. When both players take the optimal strategy to maximize their scores, find Alice's score minus Bob's score.

Constraints

N is an integer between 1 and 100 (inclusive).

a_i \ (1 \leq i \leq N) is an integer between 1 and 100 (inclusive).

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 a_3 ... a_N

Output

Print Alice's score minus Bob's score when both players take the optimal strategy to maximize their scores.

Sample Input 1

2
3 1

Sample Output 1

2

First, Alice will take the card with 3. Then, Bob will take the card with 1.
The difference of their scores will be 3 - 1 = 2.

Sample Input 2

3
2 7 4

Sample Output 2

5

First, Alice will take the card with 7. Then, Bob will take the card with 4. Lastly, Alice will take the card with 2. The difference of their scores will be 7 - 4 + 2 = 5. The difference of their scores will be 3 - 1 = 2.

Sample Input 3

4
20 18 2 18

Sample Output 3

18

Solution in Java7 (OpenJDK 1.7.0) (judge verdict: Accepted)

import java.io.InputStreamReader;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.*;
import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.InputStream;
import static java.lang.Math.*;

public class Main {

    public static void main(String[] args) {
        final String[] tasks = new String[]{"D","C","B","A"};
        for(final String task:tasks) {
            try {
                Class ca = Main.class.getClassLoader().loadClass(task);
                if (ca.getField("on").getInt(null) == 1) {
                    Object aTask = ca.newInstance();
                    Method m = ca.getMethod("S", null);
                    m.invoke(aTask, null);
                }
            } catch (Exception ex) { }
        }
    }

}

class A {
    public static int on = 1;

    public void run(){
        int n = ni();
        int[] a = new int[n];
        for(int i=0;i<n;i++){
            a[i] = ni();
        }
        Arrays.sort(a);
        int s1 = 0;
        int s2 = 0;
        boolean al = true;
        for(int i=n-1;i>=0;i--){
            if(al) {
                s1 += a[i];
            }else{
                s2 += a[i];
            }
            al = !al;
        }
        pl(s1-s2);




    }
    private InputReader in =  new InputReader(System.in);
    private PrintWriter out = new PrintWriter(System.out);
    public void S(){run();out.close(); }
    public int ni(){return Integer.parseInt(in.ns());}
    public long nl(){return Long.parseLong(in.ns());}
    public String ns(){return in.ns();}
    public void p(Object obj){out.print(obj);}
    public void ps(Object obj){p(obj);p(" ");}
    public void pl(Object obj){out.println(obj);}
    public int gcd(int a,int b){ while( b != 0 ) { int t = a % b;a = b;b = t; } return a; }
}

class B {
    public static int on = 0;

    public void run(){

    }
}

class InputReader {
    private BufferedReader reader;
    private StringTokenizer tokenizer;

    public InputReader(InputStream stream) {
        reader = new BufferedReader(new InputStreamReader(stream), 32768);
        tokenizer = null;
    }

    public String ns() {
        while (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }

}