strs = gets.chomp.split("").map(&:to_s)
list = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m"]
diff = list - strs.uniq
if diff.length > 1
	puts "Inpossible" 
elsif diff.length == 0
	puts strs.sort
else
	puts diff
end