#!/usr/bin/env python
import fileinput
import itertools
import numpy as np
from collections import Counter


txt_input = []

txt_input = input()

S = list(txt_input[0])

S.sort()

#print(S)
count = 0
lst =[]
letter = ''

S_unique = list(set(S))
if len(S) - len(S_unique) == 6:
    dct = Counter(S)
    search_letter = 1
    for name, age in dct.items():
        if age == search_letter:
            print(name)
        else:
            break
else:
    print('Impossible')