N, M = gets.split.map(&:to_i)
A = gets.split.map(&:to_i)
B = gets.split.map(&:to_i)

if (A & B).empty?
  puts -1
else
  (N * M).times do |i|
    next unless A[i % N] == B[i % M]

    puts i + 1
    break
  end
end