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