var
a,b,c,p:real;
begin
read(a,b,c);
p:=(a+b+c)/2;
p:=sqrt(p*(p-a)*(p-b)*(p-c));
writeln('S=',p);
end.
var
a,b,c,p:real;
begin
read(a,b,c);
p:=(a+b+c)/2;
p:=sqrt(p*(p-a)*(p-b)*(p-c));
writeln('S=',p);
end.