uses
  SysUtils ,Math;

Var
  a, R:integer;
  s :Real;
begin
  ReadLn(a,R);
  If R > 0.5*a then
    S := pi*R*R + 2*a*sqrt(R*R-0.25*a*a) -4*R*R*arcCos(0.5*a/R);
  else S := pi * R*R;
  WriteLn(S :0:3);
end.