uses math;
const p=3.14; {   -> p = pi , it will more accurate}
var a,r:integer;
    s,angl,cosa:real;
begin
  readln (a,r);
  if (2*r<a) then
    s:=p*r*r
  else
    if (sqrt(2)*r>a) then
      s:=a*a
    else
      begin
        cosa:=a/(2*r);
        angl:=2*arctan(cosa);
        angl:=p/2-angl;
        s:=((a/2)*sqrt(r*r-(a*a)/4))+angl*r*r/2;
        s := s * 4;
      end;
   writeln (s:10:3);
end.

Oh my friend.Even though I try my best.
I still get 10 WA before I got AC with your program  8::::(
What a hard work....:-)
First of all
I use p=3.1415926535897
.......A terrible number, isn't it?
Then
if (2*r<a)  ==> if (2*r<=a)
if (sqrt(2)*r>a) ==> if (sqrt(2)*a/2<r) then
angl:=2*arctan(cosa); ==> angl:=2*arccos(cosa);
writeln (s:10:3); ===>  writeln (s:0:3);
Good luck next time.
By the way .I send a E-mail to you .
Reply it Ok??????

>

> By the way my E-mail is fc_rainofstar_@163.com
Send a E-mail to me Ok?