# 数値は別の提出がチェックしていたはず

firstline = gets.chomp!
abort "line1 format error" unless /^\d+ \d+$/=~firstline
n,m = firstline.split.map(&:to_i)

m.times{|i|
    line = gets
    abort "idx#{i} return error" unless line.chomp!
    abort "idx#{i} format error" unless /^\d+ \d+$/=~line
}

abort "end of line error" if gets

puts "Impossible"