program main
  implicit none
  integer(4) n,l,i,k
  integer(4),allocatable::a(:),r(:)
  read*,n,l
  allocate(a(n),r(n))
  read*,a(:)
  i=maxloc(a(2:)+a(1:n-1),1)
  if (a(i)+a(i+1).lt.l)then
     print*,trim("Impossible")
  else
     print*,"Possible"
     print*,(/(k,k=1,i-1),(k,k=n-1,i,-1)/)
  endif
end program main
