import java.util.*;
import java.lang.*;
import java.io.*;

class Ideone{
    public static void main(String[] args) throws Exception{
        // your code goes here
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] lines = br.readLine().split(" ");
        double a = Double.parseDouble(lines[0]);
        double b = Double.parseDouble(lines[1]);
        double x = Double.parseDouble(lines[2]);
        double y = Double.parseDouble(lines[3]);
        
        if(a*y > b*x){
            System.out.println(x + x*a/b);
        }else{
            System.out.println(y + y*a/b);
        }
    }
}