s = input()
r = "abcdefghijklm"
z,o,t = '','',''
for x in r:
	if s.count(x)==0: z+=x
	elif s.count(x)==1: o+=x
	else: t+=x
if len(z)==len(t)==1: print(z)
elif len(z)==len(t)==0: 
	for x in list(o): print(x)
else: print("Impossible")