m={}
2.times do
  gets.to_i.times do
    s = gets.chomp
    s[0...-1].chars.each_with_index do |c, i|
      m[c] = s[i+1]
    end
    m[s[-1]] ||= nil;
  end
end
case m.to_a.map(&:last).count(nil)
when 1
  c = nil
  s = ""
  while m.key(c) do
    s << m.key(c)
    c = m.key(c)
  end
  puts s.reverse
else
  puts -1
end