/**  this is a comment line in the sample program **/

 REAL f2(REAL x, REAL y ) 
 BEGIN 
    REAL z; 
    z := x*x - y*y;
    RETURN z; 
 END 
 INT MAIN f1() 
 BEGIN
    INT x;
    READ(x, "A41.input");
    INT y;
    READ(y, "A42.input");
    REAL z;
    z := f2(x,y) + f2(y,x)*0.5;
    WRITE (z, "A4.output"); 
 END