import tables let s = stdin.readLine var d = initCountTable[char]() for c in s: if c notin 'a'..'m': continue d.inc c if d.len == 13: for c in 'a'..'m': echo c elif d.len == 12 and d.largest.val == 2: for c in 'a'..'m': if not d.haskey(c): echo c break else: echo "Impossible"