coffee_tea = gets.split.map(&:to_f)

if coffee_tea[0] > coffee_tea[1]
  s = (coffee_tea[2]/coffee_tea[0]) * coffee_tea[1] + coffee_tea[2]
  puts s
elsif coffee_tea[1] > coffee_tea[0]
  s = (coffee_tea[3]/coffee_tea[1]) * coffee_tea[0] + coffee_tea[3]
  puts s
elsif coffee_tea[0] == coffee_tea[1]
  if coffee_tea[2] > coffee_tea[3]
    s = coffee_tea[3] * 2
    puts s
  else
    s = coffee_tea[2] * 2
    puts s
  end
end