import java.util.Scanner;

public class No236 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int x = sc.nextInt();
		int y = sc.nextInt();
		
		double w1=x*b/a - y;
		double w2=y*a/b - x;
		
		double d;
		
		if(w1<0){
			d = (double)x*b/a + x;
		}else if(w2<0){
			d = (double)y*a/b + y;
		}else{
			d = x+y;
		}
		
		System.out.printf("%.8f\n", d);
	}

}