program ArieTriunghi;
var a,b,c,s:real;
procedure Heron(a,b,c:real; var s:real);
var p: real;
begin
p:=(a+b+c)/2;
s:=sqrt(p*(p-a)*(p-b)*(p-c));
end;
begin {programul principal}
write('a='); read(a);
write('b='); read(b);
write('c='); read(c);
Heron(a,b,c,s);
writeln(' Aria triunghiului= ', s);
end.