program knot_puzzle
  implicit none
  integer :: n, i, j
  integer(8) :: l, a(100000)
  a = 0_8
  read(*,*) n, l
  read(*,*) a(1:n)
  j = -1
  do i = 1, n-1
    if (a(i)+a(i+1).ge.l) then
      j = i
    end if
  end do
  if (j.lt.0) then
    write(*,'(a)') "Impossible"
    stop
  end if
  write(*,'(a)') "Possible"
  do i = 1, j-1
    write(*,'(i0)') i
  end do
  do i = n-1, j, -1
    write(*,'(i0)') i
  end do
  stop
end program knot_puzzle