#!/usr/bin/env python3
t = 'abcdefghijklm'
s = input()
result = 'Impossible'
if len(s) == len(t):
    unused = ''
    for c in t:
        if c not in s:
            unused += c
    if len(unused) == 0:
        result = '\n'.join(list(t))
    elif len(unused) == 1:
        result = unused
print(result)