import java.io.*; 
public class A4 { 
    static BufferedReader $br;
    static BufferedWriter $bw;
    static double $tmp_real;
static double f2(double x, double y) throws Exception 
{   double z; 
  z=x*x-y*y; 
  return z; 

 }

public static void main(String [] args) throws Exception
{   int x; 
  $br=new BufferedReader(new FileReader("A41.input"));
    x=new Integer($br.readLine()).intValue();; 
   int y; 
  $br=new BufferedReader(new FileReader("A42.input"));
    y=new Integer($br.readLine()).intValue();; 
   double z; 
  z=f2(x, y)+f2(y, x)*0.5; 
  $tmp_real=z;
$bw=new BufferedWriter(new FileWriter("A4.output"));
    $bw.write(""+ $tmp_real);
    $bw.close();; 

 }}