program Project2;

{$APPTYPE CONSOLE}

var
a,b,c:integer;
p,s:real;
begin
readln(a,b,c);
p:=(a+b+c)/2;
if (p<a) or (p<b) or (p<c) then writeln('trukyk ne isnye')
else begin s:=sqrt(p*(p-a)*(p-b)*(p-c)) ;writeln(s);  end;
readln;
end.