(in-package :cl-user)
(eval-when (:compile-toplevel :load-toplevel :execute)
  (sb-int:defconstant-eqx opt
    #+swank '(optimize (speed 3) (safety 2))
    #-swank '(optimize (speed 3) (safety 0) (debug 0))
    #'equal)
  #+swank (ql:quickload '(:cl-debug-print :fiveam) :silent t)
  #-swank (set-dispatch-macro-character
           #\# #\> (lambda (s c p) (declare (ignore c p)) `(values ,(read s nil nil t)))))
#+swank (set-dispatch-macro-character #\# #\> #'cl-debug-print:debug-print-reader)

(macrolet ((def-int (b)
             `(progn (deftype ,(intern (format nil "UINT~A" b)) () '(unsigned-byte ,b))
                     (deftype ,(intern (format nil "INT~A" b)) () '(signed-byte ,b))))
           (defs (&rest bits) `(progn ,@(mapcar (lambda (b) `(def-int ,b)) bits))))
  (defs 2 4 7 8 15 16 31 32 62 63 64))

(defconstant +mod+ 1000000007)

(defmacro dbg (&rest forms)
  #+swank (if (= (length forms) 1)
              `(format *error-output* "~A => ~A~%" ',(car forms) ,(car forms))
              `(format *error-output* "~A => ~A~%" ',forms `(,,@forms)))
  #-swank (declare (ignore forms)))

(declaim (inline println))
(defun println (obj &optional (stream *standard-output*))
  (let ((*read-default-float-format* 'double-float))
    (prog1 (princ obj stream) (terpri stream))))

;; BEGIN_INSERTED_CONTENTS
;;;
;;; Binomial coefficient with mod
;;; build: O(n)
;;; query: O(1)
;;;

(defpackage :cp/binomial-coefficient-mod
  (:use :cl)
  (:export #:binom #:perm #:multinomial #:stirling2 #:catalan #:+binom-mod+
           #:*fact* #:*fact-inv* #:*inv*))
(in-package :cp/binomial-coefficient-mod)

;; TODO: non-global handling

(defconstant +binom-size+ 510000)
(defconstant +binom-mod+ (if (boundp 'cl-user::+mod+)
                             (symbol-value 'cl-user::+mod+)
                             #.(+ (expt 10 9) 7)))

(sb-ext:define-load-time-global *fact*
    (make-array +binom-size+ :element-type '(unsigned-byte 31))
    "table of factorials")
(sb-ext:define-load-time-global *fact-inv*
    (make-array +binom-size+ :element-type '(unsigned-byte 31))
    "table of inverses of factorials")
(sb-ext:define-load-time-global *inv*
    (make-array +binom-size+ :element-type '(unsigned-byte 31))
    "table of inverses of non-negative integers")
(declaim ((simple-array (unsigned-byte 31) (*)) *fact* *fact-inv* *inv*))

(defun initialize-binom ()
  (declare (optimize (speed 3) (safety 0)))
  (setf (aref *fact* 0) 1
        (aref *fact* 1) 1
        (aref *fact-inv* 0) 1
        (aref *fact-inv* 1) 1
        (aref *inv* 1) 1)
  (loop for i from 2 below +binom-size+
        do (setf (aref *fact* i) (mod (* i (aref *fact* (- i 1))) +binom-mod+)
                 (aref *inv* i) (- +binom-mod+
                                   (mod (* (aref *inv* (rem +binom-mod+ i))
                                           (floor +binom-mod+ i))
                                        +binom-mod+))
                 (aref *fact-inv* i) (mod (* (aref *inv* i)
                                             (aref *fact-inv* (- i 1)))
                                          +binom-mod+))))

(initialize-binom)

(declaim (inline binom))
(defun binom (n k)
  "Returns nCk."
  (if (or (< n k) (< n 0) (< k 0))
      0
      (mod (* (aref *fact* n)
              (mod (* (aref *fact-inv* k) (aref *fact-inv* (- n k))) +binom-mod+))
           +binom-mod+)))

(declaim (inline perm))
(defun perm (n k)
  "Returns nPk."
  (if (or (< n k) (< n 0) (< k 0))
      0
      (mod (* (aref *fact* n) (aref *fact-inv* (- n k))) +binom-mod+)))

;; TODO: compiler macro or source-transform
(declaim (inline multinomial))
(defun multinomial (&rest ks)
  "Returns the multinomial coefficient K!/k_1!k_2!...k_n! for K = k_1 + k_2 +
... + k_n. K must be equal to or smaller than
MOST-POSITIVE-FIXNUM. (multinomial) returns 1."
  (let ((sum 0)
        (result 1))
    (declare ((integer 0 #.most-positive-fixnum) result sum))
    (dolist (k ks)
      (incf sum k)
      (setq result
            (mod (* result (aref *fact-inv* k)) +binom-mod+)))
    (mod (* result (aref *fact* sum)) +binom-mod+)))

(declaim (inline stirling2))
(defun stirling2 (n k)
  "Returns the stirling number of the second kind S2(n, k). Time complexity is
O(klog(n))."
  (declare ((integer 0 #.most-positive-fixnum) n k))
  (labels ((mod-power (base exp)
             (declare ((integer 0 #.most-positive-fixnum) base exp))
             (loop with res of-type (integer 0 #.most-positive-fixnum) = 1
                   while (> exp 0)
                   when (oddp exp)
                   do (setq res (mod (* res base) +binom-mod+))
                   do (setq base (mod (* base base) +binom-mod+)
                            exp (ash exp -1))
                   finally (return res))))
    (loop with result of-type fixnum = 0
          for i from 0 to k
          for delta = (mod (* (binom k i) (mod-power i n)) +binom-mod+)
          when (evenp (- k i))
          do (incf result delta)
             (when (>= result +binom-mod+)
               (decf result +binom-mod+))
          else
          do (decf result delta)
             (when (< result 0)
               (incf result +binom-mod+))
          finally (return (mod (* result (aref *fact-inv* k)) +binom-mod+)))))

(declaim (inline catalan))
(defun catalan (n)
  "Returns the N-th Catalan number."
  (declare ((integer 0 #.most-positive-fixnum) n))
  (mod (* (aref *fact* (* 2 n))
          (mod (* (aref *fact-inv* (+ n 1))
                  (aref *fact-inv* n))
               +binom-mod+))
       +binom-mod+))

;;;
;;; Arithmetic operations with static modulus
;;;

(defpackage :cp/mod-operations
  (:use :cl)
  (:export #:define-mod-operations))
(in-package :cp/mod-operations)

;; NOTE: Currently MOD* and MOD+ doesn't apply MOD when the number of
;; parameters is one. For simplicity I won't fix it for now.
(defmacro define-mod-operations (divisor)
  (let ((mod* (intern "MOD*"))
        (mod+ (intern "MOD+"))
        (incfmod (intern "INCFMOD"))
        (decfmod (intern "DECFMOD"))
        (mulfmod (intern "MULFMOD")))
    `(progn
       (defun ,mod* (&rest args)
         (reduce (lambda (x y) (mod (* x y) ,divisor)) args))

       (defun ,mod+ (&rest args)
         (reduce (lambda (x y) (mod (+ x y) ,divisor)) args))

       #+sbcl
       (eval-when (:compile-toplevel :load-toplevel :execute)
         (locally (declare (sb-ext:muffle-conditions warning))
           (sb-c:define-source-transform ,mod* (&rest args)
             (if (null args)
                 1
                 (reduce (lambda (x y) `(mod (* ,x ,y) ,',divisor)) args)))
           (sb-c:define-source-transform ,mod+ (&rest args)
             (if (null args)
                 0
                 (reduce (lambda (x y) `(mod (+ ,x ,y) ,',divisor)) args)))))

       (define-modify-macro ,incfmod (delta)
         (lambda (x y) (mod (+ x y) ,divisor)))

       (define-modify-macro ,decfmod (delta)
         (lambda (x y) (mod (- x y) ,divisor)))

       (define-modify-macro ,mulfmod (multiplier)
         (lambda (x y) (mod (* x y) ,divisor))))))

;; BEGIN_USE_PACKAGE
(eval-when (:compile-toplevel :load-toplevel :execute)
  (use-package :cp/mod-operations :cl-user))
(eval-when (:compile-toplevel :load-toplevel :execute)
  (use-package :cp/binomial-coefficient-mod :cl-user))
(in-package :cl-user)

;;;
;;; Body
;;;

(define-mod-operations +mod+)
(defun main ()
  (let* ((s (read))
         (res 0))
    (loop for k from 1
          while (<= (* 3 k) s)
          do (incfmod res (binom (+ (- s (* 3 k)) (- k 1))
                                 (- k 1))))
    (println res)))

#-swank (main)

;;;
;;; Test and benchmark
;;;

#+swank
(defun get-clipbrd ()
  (with-output-to-string (out)
    #+os-windows (run-program "powershell.exe" '("-Command" "Get-Clipboard") :output out :search t)
    #+os-unix (run-program "xsel" '("-b" "-o") :output out :search t)))

#+swank (defparameter *this-pathname* (uiop:current-lisp-file-pathname))
#+swank (defparameter *dat-pathname* (uiop:merge-pathnames* "test.dat" *this-pathname*))

#+swank
(defun run (&optional thing (out *standard-output*))
  "THING := null | string | symbol | pathname

null: run #'MAIN using the text on clipboard as input.
string: run #'MAIN using the string as input.
symbol: alias of FIVEAM:RUN!.
pathname: run #'MAIN using the text file as input."
  (let* ((*standard-output* (or out (make-string-output-stream)))
         (res (etypecase thing
                (null
                 (with-input-from-string (*standard-input* (delete #\Return (get-clipbrd)))
                   (main)))
                (string
                 (with-input-from-string (*standard-input* (delete #\Return thing))
                   (main)))
                (symbol (5am:run! thing))
                (pathname
                 (with-open-file (*standard-input* thing)
                   (main))))))
    (if out res (get-output-stream-string *standard-output*))))

#+swank
(defun gen-dat ()
  (uiop:with-output-file (out *dat-pathname* :if-exists :supersede)
    (format out "")))

#+swank
(defun bench (&optional (out (make-broadcast-stream)))
  (time (run *dat-pathname* out)))

#-swank
(eval-when (:compile-toplevel)
  (when (and (boundp 'sb-c::*compiler-warning-count*)
             (> sb-c::*compiler-warning-count* 0))
    (sb-ext:quit :unix-status 1)))

;; To run: (5am:run! :sample)
#+swank
(it.bese.fiveam:test :sample
  (it.bese.fiveam:is
   (equal "3
"
          (run "7
" nil)))
  (it.bese.fiveam:is
   (equal "0
"
          (run "2
" nil)))
  (it.bese.fiveam:is
   (equal "294867501
"
          (run "1729
" nil))))


Measured memory_bytes: 31256