(let* ((n (read)))
  (define vec (make-vector (+ n 1) 0))
  (vector-set! vec 0 1)

  (print (let loop ((i 1))
	   (cond ((< n i) (vector-ref vec n))
		 (else
		  (let1 num #?=(+ (if (>= (- i 1) 0)
				      (vector-ref vec (- i 1))
				      0
				      )
				  (if (>= (- i 2) 0)
				      (vector-ref vec (- i 2))
				      0))
			(vector-set! vec i num)
			(loop (+ i 1))))))))