# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	S = input()
	if len(S) <= 12:
		print("Impossible")
		return

	table = [0] * 13
	for i in S:
		table[ord(i) - 97] = 1

	if sum(table) <= 11:
		print("Impossible")
		return

	if sum(table) == 13:
		for i in range(13):
			print(chr(97 + i))

		return

	ans = table.index(0)
	print(chr(97 + ans))


if __name__ == '__main__':
	main()