Var x1, x2, x3, x4, y1, y2, y3, y4, a, b: real;
begin
//A(x1; y1) B(x2; y2) C(x3; y3) D(x4; y4)
(*
A------B
| |
| |
C------ D
*)
read(x1, y1, x2, y2, x3, y3, x4, y4);
a := sqrt(sqr(x2 - x1) + sqr(y2 - y1));
b := sqrt(sqr(x3 - x1) + sqr(y3 - y1));
writeln(a*b);
end.