program main
	implicit none
    integer(8)::n,i,j,k,b,c
    integer(8),allocatable::a(:)
    read(*,*)n
    allocate(a(n))
    read(*,*) a
    call heapsort(n,a)
    !write(*,*) a
    k=a(n)
    b=0
    c=0
    do i=n-1,1,-1
    	if(a(i)==k)then
        	if (b==0)then
        		b=k
                k=0
            else if(c==0)then
            	c=k
                k=0
            end if
        else
        	k=a(i)
        end if
    end do
    write(*,*) c*b
    
    deallocate(a)
    stop
contains
subroutine heapsort(n,array)
        implicit none
        integer(8),intent(in) :: n
        integer(8),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 main


