program Project1;

{$APPTYPE CONSOLE}

var a,b,c,s,p:real;

f1,f2:text;
begin
assign(f1,'input.txt');
reset(f1);
readln(f1,a,b,c);
p:=(a+b+c)/2;
s:=sqrt(p*(p-a)*(p-b)*(p-c));
close(f1);
assign(f2,'output.txt');
rewrite(f2);
writeln(f2,'s=',s:2:2);
close(f2);
end.