T = "abcdefghijklm"
S = input()

if len(set(list(S))) == 13:
    for t in T:
        print(t)
    exit(0)

    
if len(set(list(S))) <= 11:
    print("Impossible")
    exit(0)
    
lack = (set(list(T)) - set(list(S))).pop()

print(lack)