Program Geron;
Var a, b, c, p, s: real;
Begin
 writeln ('   : ');
 readln (a, b, c);
 p:=(a+b+c)/2;                 //
 s:=sqrt(p*(p-a)*(p-b)*(p-c)); // 
 writeln ('  ', s:7:2);
End.