s = list(input())
moto=list('abcdefghijklmnopqrstuvwxyz')

x=''
y=''
a=0

for abc in moto:
  if abc in s:
    continue
  else:
    x=abc
    break

for _ in s:
  if s[a]==moto[a]:
    a+=1
  else:
    y=s[a]

txt=x+'to'+y

print(txt)