program main
  implicit none
  integer::i,j,N
  integer,allocatable::A(:),Bx(:),By(:)
  
  read(*,*)N
  allocate(A(1:N),Bx(1:N-1),By(1:N-1))
  read(*,*)A(1:N)
  call heapsort(N,A)
  
  do i=1,N-2
     Bx(i)=A(1)
     By(i)=A(N-i+1)
     A(1)=A(1)-A(N-i+1)
  enddo
  Bx(N-1)=A(2)
  By(N-1)=A(1)
  A(1)=A(2)-A(1)
  write(6,*)A(1)
  
  do i=1,N-1
     write(6,*)Bx(i),By(i)
  enddo
  
  stop
end program main

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
