import scala.io.StdIn.readLine
import scala.collection.mutable.PriorityQueue
import scala.annotation.tailrec

// PriorityQueue[Long]()(scala.math.Ordering.Long.reverse)
object Lib {
  object Number {
    // @return Array length is equal to 'n'.
    //  Kth element of Array is true if K is prime else false.
    final def sieve(n : Int) : Array[Boolean] = {
      val isprime = Array.fill(n+1)(true)
      isprime(0) = false
      isprime(1) = false
      for(i <- 2 to Math.ceil(Math.sqrt(n.toDouble)).toInt;
          if isprime(i);
          j <- i*i to n by i){
        isprime(j) = false
      }
      isprime
    }
    // @return Array of primes that is less than or equal to n
    final def primes(n : Int) : Array[Int] =
      sieve(n).zipWithIndex.withFilter(_._1).map(_._2)
  }
  object EnRich {
    implicit class AString(val self : String) extends AnyVal {
      def splitToIntArray = self.split(" ").map(_.toInt)
    }
  }
}

import Lib.EnRich._
object Main {
  def main(args : Array[String]) : Unit = {
    val (a,b,x,y) = {
      val abxy = readLine().splitToIntArray.map(_.toDouble)
      (abxy(0),abxy(1),abxy(2),abxy(3))
    }

    val ret = if(x/a <= y/b) x+x/a*b // many cofee
              else y+y/b*a //many tea

    println(ret)
  }
}