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 C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>

int main(void) 
{
	int n;
	int a[100];
	int i, j;
	int max, num;
	int* pnum;
	int alice = 0;
	int bob = 0;

	//入力部分　始まり
	scanf("%d", &n);

	for ( i = 0; i < n; i++)
	{
		scanf("%d", &a[i]);
	}
	//入力部分　終わり

	//処理部分　始まり
	for (i = 0; i < n; i++)
	{
		max = 0;
		num = 0;
		pnum = &num; //pnumはnumのアドレス

		for (j = 0; j < n; j++)
		{
			if (max < a[j])//参照した値がmaxより大きい場合
			{
				max = a[j];//maxを参照した値に置き換える
				*pnum = j; //ifの外にあるnumに値を返したいのでポインタを使う

			}

			if (j == n - 1) //n番目まで比較したら一番大きい要素の中身を0に変える
			{
				a[num] = 0;
			}
			
		}

		//1回おきにAliceとBobに代入
		if (i % 2 == 0)
		{
			alice += max;
		}
		else
		{
			bob += max;
		}
		
	}
	//処理部分終わり

	printf("%d", alice - bob);

	return 0;
}