s = gets.chop
map = Hash.new
s.chars.each do |c|
    unless 'a' <= c and c <= 'm'
        puts "Impossible"
        exit
    end
    if map.has_key?(c)
        map[c] = map[c] + 1
    else
        map[c] = 1
    end
end

if map.size == 13
    "abcdefghijklm".chars.each do |c|
        puts c
    end
elsif map.size == 12
    "abcdefghijklm".chars.each do |c|
        unless map.has_key?(c)
            puts c
        end
    end
else
    puts "Impossible"
end