# -*- coding: utf-8 -*-
"""
No.548 国士無双
https://yukicoder.me/problems/no/548

"""
import sys
from sys import stdin
input = stdin.readline


def solve(S):
    res = []

    for c in "abcdefghijklm":
        T = S + c
        d = [0] * 13
        match = True
        for t in T:
            if 'a' <= t <= 'm':
                d[ord(t)-ord('a')] += 1
            else:
                match = False
                break
        if max(d) > 2 or min(d) < 1:
            match = False
        if match:
            res.append(c)
    return res


def main(args):
    S = input().strip()
    res = solve(S)
    if res == []:
        print("Impossible")
    else:
        print(*res, sep='\n')


if __name__ == '__main__':
    main(sys.argv[1:])