n,l=list(map(int,input().split()))

a=list(map(int,input().split()))

last=-1

for i in range(n-1):

  if a[i]+a[i+1]>=l:

    last=i+1

    break

if last==-1:

  print("Impossible")

else:

  print("Possible")

  for i in range(1,last):

    print(i)

  for i in range(len(a)-1,last-1,-1):

    print(i)

import sys

readline = sys.stdin.readline



N,L = list(map(int,readline().split()))

A = list(map(int,readline().split()))



# 2個でL以上の隣合うペアがどこかにあれば、そこを最後に残せば大丈夫

target = -1

for i in range(1,len(A)):

  if A[i] + A[i - 1] >= L:

    target = i

    break

if target == -1:

  print("Impossible")

  exit(0)



left = []

for i in range(1,target):

  left.append(i)

  

right = []

for i in range(len(A) - 1,target,-1):

  right.append(i)



print("Possible")

for l in left:

  print(l)

for r in right:

  print(r)

print(target)
n, l = list(map(int, input().split()))
a = list(map(int, input().split()))
last = -1
for i in range(n - 1):
    if a[i] + a[i + 1] >= l:
        last = i + 1
        break
if last == -1:
    print("Impossible")
else:
    print("Possible")
    for i in range(1, last):
        print(i)
    for i in range(len(a) - 1, last - 1, -1):
        print(i)

import sys

readline = sys.stdin.readline
N, L = list(map(int, readline().split()))
A = list(map(int, readline().split()))
# 2個でL以上の隣合うペアがどこかにあれば、そこを最後に残せば大丈夫
target = -1
for i in range(1, len(A)):
    if A[i] + A[i - 1] >= L:
        target = i
        break
if target == -1:
    print("Impossible")
    exit(0)
left = []
for i in range(1, target):
    left.append(i)
right = []
for i in range(len(A) - 1, target, -1):
    right.append(i)
print("Possible")
for l in left:
    print(l)
for r in right:
    print(r)
print(target)

-n, l = list(map(int, input().split())) -a = list(map(int, input().split())) -last = -1 -for i in range(n - 1): -    if a[i] + a[i + 1] >= l: -        last = i + 1 +import sys + +readline = sys.stdin.readline +N, L = list(map(int, readline().split())) +A = list(map(int, readline().split())) +# 2個でL以上の隣合うペアがどこかにあれば、そこを最後に残せば大丈夫 +target = -1 +for i in range(1, len(A)): +    if A[i] + A[i - 1] >= L: +        target = i -if last == -1: +if target == -1: -else: -    print("Possible") -    for i in range(1, last): -        print(i) -    for i in range(len(a) - 1, last - 1, -1): -        print(i) +    exit(0) +left = [] +for i in range(1, target): +    left.append(i) +right = [] +for i in range(len(A) - 1, target, -1): +    right.append(i) +print("Possible") +for l in left: +    print(l) +for r in right: +    print(r) +print(target)