A, B = 2.times.map do
  gets.to_i.times.map do
    gets.chomp
  end
end

pf = A.map { |a| a[0] } & B.map { |b| b[0] }
(p -1; exit) if pf.size > 1
z = pf[0]
x = A.find { |a| a[0] == z }
y = B.find { |b| b[0] == z }
until x.size == y.size
  x += A.find { |a| a[0] == y[x.size] } while x.size < y.size
  y += B.find { |b| b[0] == x[y.size] } while y.size < x.size
end
puts x