A="abcdefghijklm"
S=input()

D={a:0 for a in A}
for s in S:
    D[s]+=1

K=0
for a in A:
    K+=(D[a]==0)

if K>=2:
    print("Impossible")
elif K==1:
    print(min(D,key=lambda x:D[x]))
else:
    for a in A:
        print(a)