import java.util.*;

public class Exercise66{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    double a = sc.nextInt();

    double b = sc.nextInt();

    double x = sc.nextInt();

    double y = sc.nextInt();

    double sum = 0;

    if(a == b){
      double min = Math.min(x, y);
      sum = min * 2;
      int sumd = (int)sum;
      System.out.println(sumd);
    }else{
      double xd = (y * a) / b;
      if (xd > x){
        double yd = (x * b) /a;
        sum = x + yd;
      }else{
        sum = y + xd;
      }
      System.out.println(sum);
    }
  }
}