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

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)

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)

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
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)

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)

+        break