from collections import defaultdict

d = defaultdict(int)

try:
    
    S = input()
    
except:
    
    print('Impossible')
    exit()
    
if len(S) != 13:
    
    print('Impossible')
    exit()
    
for s in S:
    
    d[s] += 1
    
x = list(d.values())

if x.count(1) == 13:
    
    print('a', 'b', 'c', 'd','e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', sep='\n')
    
elif x.count(1) == 11:
    
    for k in 'abcdefghijklm':
        if not (k in S):
            print(k)
            break
        
else:
    
    print('Impossible')