program main

  implicit none

  integer    :: n,k
  integer(8),allocatable :: a(:)

  integer    :: i,j,pn
  integer(8),allocatable :: p(:)

  read(*,*) n, k
  allocate( a(n) )
  allocate( p(n*(n-1)/2) )
  read(*,*) a

  pn = 0
  do i = 1, n
    do j = i+1, n
      pn = pn + 1
      p(pn) = a(i) * a(j)
    end do
  end do
  
  call quicksort1( p, 1, n*(n-1)/2 ) 

  print*, p(k)

end program main

recursive subroutine quicksort1(a, first, last)
  implicit none
  integer(8),intent(inout)::a(*)
  integer,intent(in)::first,last
  !
  ! Original
  ! https://gist.github.com/t-nissie/479f0f16966925fa29ea
  !
  integer(8)::x,t
  integer::i,j

  x = a((first+last)/2)
  i = first
  j = last
  do
     do while (a(i) < x)
        i=i+1
     end do
     do while (x < a(j))
        j=j-1
     end do
     if (i >= j) exit
     t = a(i)
     a(i) = a(j)
     a(j) = t
     i=i+1
     j=j-1
  end do
  if (first < i-1) call quicksort1(a, first, i-1)
  if (j+1 < last)  call quicksort1(a, j+1, last)

  return
end subroutine quicksort1
