#-sbcl (error "This only works using SBCL")
(declaim (optimize (speed 3)
                   (compilation-speed 0)
                   (debug 0)
                   (safety 0)))

(defun pidigits (x-digits)
  (macrolet ((gen-arccot (sign opposite)
			 `(,(intern (format nil "~a~a" 'arccot sign)) (x-rest n x-elevate product)
			   (declare (type integer x-rest n))
			   (declare (type bignum x-elevate product))
			   (let ((term (floor x-elevate n)))
			     (if (zerop term)
				 product
			       (,(intern (format nil "~a~a" 'arccot opposite)) x-rest (+ n 2)
				(the bignum (floor x-elevate x-rest))
				(the bignum (,(intern (format nil "~a" sign)) product term )))))))
	     (labels ((gen-arccot + -)
		      (gen-arccot - +))
		     (let* ((limit (expt 10 (+ 10 x-digits)))
			    (first-thread (sb-thread:make-thread
					   (lambda () (* 44 (the bignum (arccot+ 3249 1 (the bignum (floor limit 57)) 1))))))
			    (second-thread (sb-thread:make-thread
					    (lambda () (* 7 (the bignum (arccot+ 57121 1 (the bignum (floor limit 239)) 1))))))
			    (third-thread (sb-thread:make-thread
					   (lambda () (* -12 (the bignum (arccot+ 465124 1 (the bignum (floor limit 682)) 1))))))
			    (fourth-thread (sb-thread:make-thread
					    (lambda () (* 24 (the bignum (arccot+ 167521249 1 (the bignum (floor limit 12943)) 1)))))))
		       (declare (type bignum limit))
		       (sb-thread:thread-yield)
		       (format nil "3.~a" (the bignum (rem
						       (the bignum (floor
								    (the bignum (* 4
										   (the bignum (+
												(the bignum (sb-thread:join-thread fourth-thread))
												(the bignum (sb-thread:join-thread third-thread))
												(the bignum (sb-thread:join-thread second-thread))
												(the bignum (sb-thread:join-thread first-thread))))))
								    10000000000))
						       (/ limit 10000000000))))))))


  (if (not (cadr *posix-argv*))
      (format t "Error: you should pass an argument~%")
    (let ((n (parse-integer (cadr *posix-argv*))))
      (if (not (typep n 'integer))
	  (print "The argument should be a integer~%")
	(print (pidigits n)))))