s=input()
chk={i:0 for i in 'abcdefghijklm'}
for i in s:
    if i not in chk:
        continue
    else:
        chk[i]+=1
if [*chk.values()].count(0)>1 or [*chk.values()].count(2)>1:
    print('Impossible')
elif [*chk.values()].count(1)==len('abcdefghijklm'):
    print(*[*'abcdefghijklm'],sep='\n')
else:
    for i,j in chk.items():
        if j==0:
            print(i)
            break