class Integer def divisor_list require 'prime' return [] if self <= 0 return [1] if self == 1 prime_division.map.with_index { |(base, k), i| s = i.zero? ? 0 : 1 (s..k).map { |n| base ** n } }.inject { |res, e| res + res.flat_map { |t| e.map { |v| t * v } } }.sort end end A, B = gets.split.map(&:to_i).sort (A + B).divisor_list.each do |x| next if x > A + B next if x < B - A if (A + x) % B == 0 && (B + x) % A == 0 puts x exit end end puts -1