program PR1;

{$APPTYPE CONSOLE}
 var a,b,c,p,s:real;
begin;
writeln('BEDITE a');
readln(a);
writeln('BEDITE b');
readln(b);
writeln('BEDITE c');
readln(c);
p:=(a+b+c)/2;
S:=SQRT(p*(p-a)*(p-b)*(p-c));
writeln('S=',s);
readln;
end.