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

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

for i in range(n-1):

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

    print("Possible")

    for j in range(i):print((j+1))

    for j in range(n-1,i,-1):print(j)

    exit()

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

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

if a[0]+a[1]>=l:

  print("Possible")

  for i in range(n-1,0,-1):print(i)

  exit()

if a[-2]+a[-1]>=l:

  print("Possible")

  for i in range(1,n):print(i)

  exit()

ans=-1

for i in range(1,n):

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

    ans=i

    break

if ans==-1:print("Impossible")

else:

  print("Possible")

  for i in range(1,ans):print(i)

  for i in range(n-1,ans,-1):print(i)

  print(ans)

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

n, l = list(map(int, input().split()))
a = list(map(int, input().split()))
if a[0] + a[1] >= l:
    print("Possible")
    for i in range(n - 1, 0, -1):
        print(i)
    exit()
if a[-2] + a[-1] >= l:
    print("Possible")
    for i in range(1, n):
        print(i)
    exit()
ans = -1
for i in range(1, n):
    if a[i - 1] + a[i] >= l:
        ans = i
        break
if ans == -1:
    print("Impossible")
else:
    print("Possible")
    for i in range(1, ans):
        print(i)
    for i in range(n - 1, ans, -1):
        print(i)
    print(ans)

-for i in range(n - 1): -    if a[i] + a[i + 1] >= l: -        print("Possible") -        for j in range(i): -            print((j + 1)) -        for j in range(n - 1, i, -1): -            print(j) -        exit() -print("Impossible") +if a[0] + a[1] >= l: +    print("Possible") +    for i in range(n - 1, 0, -1): +        print(i) +    exit() +if a[-2] + a[-1] >= l: +    print("Possible") +    for i in range(1, n): +        print(i) +    exit() +ans = -1 +for i in range(1, n): +    if a[i - 1] + a[i] >= l: +        ans = i +        break +if ans == -1: +    print("Impossible") +else: +    print("Possible") +    for i in range(1, ans): +        print(i) +    for i in range(n - 1, ans, -1): +        print(i) +    print(ans)