Pascal :

var a,b,c:longint;
    s,p:real;
begin
 readln(a,b,c);
 if (a+b>c) and (a+c>b) and (b+c>a) then
  begin
   p:=(a+b+c)/2;
   s:=sqrt(p*(p-a)*(p-b)*(p-c));
   writeln(s:0:2);
  end
 else
  writeln('Data Error！');
end.