integer N
integer,allocatable,dimension(:)::X
integer,allocatable,dimension(:)::ansx,ansy
integer ans
read*,N
allocate(X(N))
read*,X
call heapsort(N,X)

allocate(ansx(N-1),ansy(N-1))
if(mod(N,2)==1)then
  ansx(1)=x(1)
  ansy(1)=x(N)
  do i=2,N-1
    if(mod(i,2)==0)then
      ansx(i)=x(1+i/2)
    else
      ansx(i)=x(N-i/2)
    endif
      ansy(i)=ansx(i-1)-ansy(i-1)
  end do
else
  ansx(1)=x(N)
  ansy(1)=x(1)
  do i=2,N-1
    if(mod(i,2)==0)then
    ansx(i)=x(1+i/2)
  else
    ansx(i)=x(N-i/2)
  endif
    ansy(i)=ansx(i-1)-ansy(i-1)
  end do
endif

ans=ansx(N-1)-ansy(N-1)

print"(i0)",ans
do i=1,N-1
  print"(i0,A,i0)",ansx(i)," ",ansy(i)
end do
contains

subroutine heapsort(n,array)
  implicit none
!ここの入力は状況に応じて変更すること
  integer,intent(in) :: n
  integer,intent(inout) :: array(1:n)
  integer::i,k,j,l
  integer:: t

  l=n/2+1
  k=n
  do while(k /= 1)
     if(l > 1)then
        l=l-1
        t=array(L)
     else
        t=array(k)
        array(k)=array(1)
        k=k-1
        if(k == 1) then
           array(1)=t
           exit
        endif
     endif
     i=l
     j=l+l
     do while(j<=k)
        if(j < k)then
           if(array(j) < array(j+1))j=j+1
        endif
        if (t < 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