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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program tenquestionsix
implicit none
integer N, i, suma, sumb, sumab
integer,allocatable,dimension(:) :: A
suma=0
sumb=0
sumab=0
read(*,*) N
allocate(A(N))
read(*,*) A
call heapsort(N,A)
 do i=N,1,-2
 suma=suma+A(i)
 end do
 do i=N-1,1,-2
 sumb=sumb+A(i)
 end do
sumab=suma-sumb
write(*,*) sumab
end program

subroutine heapsort(n,array)
  implicit none
  integer,intent(in) :: n                           
  integer,intent(inout) :: array(1:n)     
  integer ::i,k,j,l
  double precision :: t
  
  if(n.le.0)then                                    
     write(6,*)"Error, at heapsort"; stop
  endif
  if(n.eq.1)return                                 

  l=n/2+1                                           
  k=n
  do while(k.ne.1)                                 
     if(l.gt.1)then
        l=l-1
        t=array(L)
     else
        t=array(k)
        array(k)=array(1)
        k=k-1
        if(k.eq.1) then
           array(1)=t
           exit
        endif
     endif
     i=l
     j=l+l
     do while(j.le.k)
        if(j.lt.k)then
           if(array(j).lt.array(j+1))j=j+1          
        endif
        if (t.lt.array(j))then                      
           array(i)=array(j)
           i=j
           j=j+j
        else
           j=k+1
        endif
     enddo 
     array(i)=t
  enddo 

  return
end subroutine heapsort