program prob3
    implicit none
    integer::N, i, j
    integer, allocatable::a(:)
    integer(16)::ans
    read(*,*) N
    allocate(a(3*N))
    read(*,*) a
    call heapsort(3*N,a)
    ans = 0
    do i = 3*N-1, N+1, -2
        ans = ans + a(i)
    end do
    write(*,*) ans
    stop
contains
    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
end program