#!/usr/bin/env python

txt_input = input()
S = list(txt_input)

S.sort()

count = 0
lst =[]
letter = ''

S_unique = list(set(S))

if len(S_unique) == 7:
    for i in range(len(S)):
        if S.count(S[i]) == 1:
            print(S[i])
            break
        else:
            pass
else:
    print('Impossible')