integer(16) N
integer(16),allocatable,dimension(:)::A
integer(16) i,T,Y,Tkouho,Ykouho
read*,N
allocate(A(N))
read*,A
call heapsort(N,A)
T=0;Y=0;Tkouho=0;Ykouho=0
do i=N,1,-1
  if(Tkouho==A(i).and.T==0)then
    T=A(i)
    Tkouho=0
  else if(Tkouho/=A(i).and.T==0)then
    Tkouho=A(i)
  else if(Ykouho/=A(i).and.Y==0)then
    Ykouho=A(i)
  else if(Ykouho==A(i).and.Y==0)then
    Y=A(i)
  else
    exit
  endif
end do
print"(i0)",Y*T
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(16),intent(in) :: n
  integer(16),intent(inout) :: array(1:n)
  integer(16)::i,k,j,l
  integer(16):: 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