uses crt;
var xa,ya,xb,yb,xc,yc,p,s,ab,bc,ac:real;
begin
clrscr;
readln(xa,ya,xb,yb,xc,yc);
ab:=sqrt(sqr(xa-xb)+sqr(ya-yb));
ac:=sqrt(sqr(xa-xc)+sqr(ya-yc));
bc:=sqrt(sqr(xb-xc)+sqr(yb-yc));
p:=(ab+bc+ac)/2;
s:=sqrt(p*(p-ab)*(p-ac)*(p-bc));
writeln(s:4:2);
readln;
end.