from string import ascii_lowercase

used = set()
while True:
	typ = input()
	if len(typ) == 1:
		reply = typ + typ
		print(reply)
		used.add(letter)
	else:
		r, w = typ.split()
		if r == '!':
			exit()
		else:
			a, b = list(w)
			used.add(a)
			used.add(b)
			flag = False
			for c in ascii_lowercase:
				if c not in used:
					reply = b + c
					print(reply)
					used.add(c)
					Flag = True
					break
			if not(flag):
				print(b + 'a')