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

a = [int(i) for i in input().split()]



max_k = 0

max_p = 0



for i in range(N-1):

    if a[i]+a[i+1] > max_k:

        max_k = a[i]+a[i+1]

        max_p = i+1



if max_k < L:

    print('Impossible')

    exit()

else:

    print('Possible')



for i in range(1, N):

    if i == max_p:

        break

    else:

        print(i)



for i in range(N-1, 0, -1):

    if i == max_p:

        print(i)

        exit()

    else:

        print(i)

N, L = map(int, input().split())

A = [int(i) for i in input().split()]



for i in range(1, N):

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

        print('Possible')

        ans = []

        for j in range(1, i):

            ans.append(j)

        for k in range(N-1, i, -1):

            ans.append(k)

        ans.append(i)

        print(*ans, sep='\n')

        exit()

print('Impossible')

N, L = list(map(int, input().split()))
a = [int(i) for i in input().split()]
max_k = 0
max_p = 0
for i in range(N - 1):
    if a[i] + a[i + 1] > max_k:
        max_k = a[i] + a[i + 1]
        max_p = i + 1
if max_k < L:
    print("Impossible")
    exit()
else:
    print("Possible")
for i in range(1, N):
    if i == max_p:
        break
    else:
        print(i)
for i in range(N - 1, 0, -1):
    if i == max_p:
        print(i)
        exit()
    else:
        print(i)

N, L = map(int, input().split())
A = [int(i) for i in input().split()]
for i in range(1, N):
    if A[i - 1] + A[i] >= L:
        print("Possible")
        ans = []
        for j in range(1, i):
            ans.append(j)
        for k in range(N - 1, i, -1):
            ans.append(k)
        ans.append(i)
        print(*ans, sep="\n")
        exit()
print("Impossible")

-N, L = list(map(int, input().split())) -a = [int(i) for i in input().split()] -max_k = 0 -max_p = 0 -for i in range(N - 1): -    if a[i] + a[i + 1] > max_k: -        max_k = a[i] + a[i + 1] -        max_p = i + 1 -if max_k < L: -    print("Impossible") -    exit() -else: -    print("Possible") +N, L = map(int, input().split()) +A = [int(i) for i in input().split()] -    if i == max_p: -        break -    else: -        print(i) -for i in range(N - 1, 0, -1): -    if i == max_p: -        print(i) +    if A[i - 1] + A[i] >= L: +        print("Possible") +        ans = [] +        for j in range(1, i): +            ans.append(j) +        for k in range(N - 1, i, -1): +            ans.append(k) +        ans.append(i) +        print(*ans, sep="\n") -    else: -        print(i) +print("Impossible")