program Project2;

{$APPTYPE CONSOLE}

var x1,x2,x3,y1,y2,y3,s,p:real;
a,b,c:real;

f1,f2:text;
begin
assign(f1,'input.txt');
reset(f1);
readln(f1,x1,x2,x3,y1,y2,y3);
a:=sqrt((x2-x1)+(y2-y1));
b:=sqrt((x3-x2)+(y3-y2));
c:=sqrt((x1-x2)+(y1-y2));
p:=(a+b+c)/2;
s:=sqrt(p*(p-a)*(p-b)*(p-c));
close(f1);
assign(f2,'output.txt');
rewrite(f2);
writeln(f2,'s=',s);
close(f2);
end.