strs = gets.chomp.split("").map(&:to_s)
list = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m"]
strs.each{ |val| list.delete(val) if strs.count(val) >= 1 }
if list.length > 1 || strs.length != 13
	puts "Inpossible" 
elsif list.length == 0
	puts strs.sort
else
	puts list
end