program Project1;
var x1,x2,y1,y2,x3,y3:integer;s:real;f:text;
begin
assign(f,'input.dat');reset(f);
readln(f,x1,y1,x2,y2,x3,y3);close(f);
assign(f,'output.sol');rewrite(f);
s:=abs((x1*y2-x2*y1)+(x2*y3-x3*y2))/2;
write(f,s:0:2);close(f);
end.