def ascan; gets.split.map(&:to_i); end
def scan; gets.to_i; end


a = gets.chomp

f = false
"a".upto("m"){|c|
    b = (a+c).chars
    h = {}
    b.each{|e| h[e]||=0; h[e]+=1}
    j = {}
    h.values.each{|e| j[e]||=0; j[e]+=1}
    if j[1] == 12 && j[2] == 1
        puts c
        f = true
    end
}

unless f
    puts "Impossible"
end