local n, l = io.read("*n", "*n")
local a = {}
for i = 1, n do
  a[i] = io.read("*n")
end
local pos = 0
for i = 1, n - 1 do
  if l <= a[i] + a[i + 1] then
    pos = i
    break
  end
end
if pos == 0 then
  print("Impossible")
else
  print("Possible")
  for i = 1, pos - 1 do
    print(i)
  end
  for i = n - 1, pos + 1, -1 do
    print(i)
  end
  print(pos)
end
