import java.util.*;
import java.util.Map.Entry;
import java.math.*;
import java.awt.geom.*;
import java.io.*;
      
      
public class Main {	

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int xa = sc.nextInt();
		int ya = sc.nextInt();
		int xb = sc.nextInt();
		int yb = sc.nextInt();
		int xa2 = -xa;
		int ya2 = ya;
		// p1 p3 y直線 Y O 
		// p2 p4      A2 B
		double S1 = ((xb - xa2) * (10000.0 - ya2) - (yb - ya2) * (0 - xa2)) / 2.0;
		double S2 = ((xb - xa2) * (ya2     - 0.0) - (yb - ya2) * (xa2 - 0)) / 2.0;
		

		double X = 0 + (0 - 10000) * S1 / (S1 + S2);
		double Y = 10000 + (0 - 10000) * S1 / (S1 + S2);
		
		System.out.printf("%.20f",Y);
		
		
	}
	
}