#!/usr/bin/env python3
t = 'abcdefghijklm'
s = input()
result = 'Impossible'
if sorted(s) == list(t):
    result = '\n'.join(list(t))
else:
    if len(s) == len(t):
        unused = ''
        for c in t:
            if c not in s:
                unused += c
        if len(unused) == 1:
            result = unused
print(result)