import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

s = list(S())
k = list("abcdefghijklm")

if len(set(s)) == 13:
    for i in k:
        print(i)
elif len(set(s)) == 12:
    d = set(k).difference(set(s))
    print(list(d)[0])
else:
    print("Impossible")