import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int A = scan.nextInt();
		int B = scan.nextInt();
		int X = scan.nextInt();
		int Y = scan.nextInt();
		scan.close();
		double k1 = (double) Y * A / B;
		double k2 = (double) X * B / A;
		double ans = 0;
		if(X - k1 >= 0) {
			ans = k1 + Y;
		}else {
			ans = k2 + X;
		}
		System.out.println(ans);
	}
}