program Ploshcha;
{$APPTYPE CONSOLE}
const k=0.5;
var a,b,c:integer;
f1,f2:text;
begin
assign(f1,'input.txt');
reset(f1);
readln(f1,a);
readln(f1,b);
readln(f1,c);
if (a+b>c) and (a+c>b) and(c+b>a) then
a:=sqrt(k*(a+b+c)*(k*(a+b+c)-a)*(k*(a+b+c)-b)*(k*(a+b+c)-c) else writeln('Ce ne trykutnyk');
assign(f2,'output.txt');
rewrite(f2);
writeln(f2,a);
close(f1);
close(f2);
end.