This is my program
program n1084;
var a, r:integer;
c, l, x, st, cosf, tgf, sinf, f, ss, st1, so, so1:real;
begin
readln(a, r);
if r<=a/2 then
 c:=3.14*r*r
else
 if r>=sqrt(a*a/2) then
  c:=a*a
 else
  begin
   l:=a/2-sqrt(r*r-a*a/4);
   x:=sqrt(2*l*l);
   st:=0.5*l*l;
   cosf:=(2*r*r-x*x)/(2*r*r);
   sinf:=sqrt(1-cosf*cosf);
   tgf:=sqrt((1/(cosf*cosf))-1);
   f:=ArcTan(tgf);
   ss:=f*r*r/2;
   st1:=0.5*r*r*sinf;
   so:=ss-st1;
   so1:=st-so;
   c:=a*a-4*so1;
  end;
write(c:0:3);
end.
When I tested it in home, answer was right. But when I send it, I have error in 2 test, Wrong Answer. Why?

Take the constant Pi with greater precision.