program abc132c
  implicit none

  integer :: n, diff
  integer, allocatable :: d(:)

  read(*,*) n
  allocate( d(n) )
  read(*,*) d(:)

  call heapsort(n, d(:))

  diff =  d(n/2+1) - d(n/2)
  print *, diff
  deallocate( d )
  stop

contains

  subroutine heapsort(n,array)
    implicit none
    integer,intent(in) :: n
    integer,intent(inout) :: array(1:n)

    integer ::i,k,j,l
    integer  :: 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

end program abc132c
