A, B = gets.chomp.split.map(&:to_i)
m = A + B

B.times do |k|
  if k <= B && (A - k) - k >= 0
    m = [m, (A - k) - k].min
  end
end

A.times do |k|
  if k <= A && (B - k) - k >= 0
    m = [m, (B - k) - k].min
  end
end

puts m