import java.util.Scanner;

public class No236 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double A = sc.nextDouble();
		double B = sc.nextDouble();
		double X = sc.nextDouble();
		double Y = sc.nextDouble();
		
		if(X/A < Y/B) {
			System.out.println(X * (A+B) / A);
		}else if(X/A > Y/B){
			System.out.println(Y * (A+B) / B);
		}else {
			System.out.println(X + Y);
		}
	}
}