(defun distance (p1 p2)
    (sqrt (+ (expt (- (first p1) (first p2)) 2) (expt (- (second p1) (second p2)) 2))))

(defun f2 (l)
    (if (cdr l) ; if this list has more than one element left
        (let ((p1 (first l)) (p2 (second l)))
            (+ (distance p1 p2) (f2 (cdr l))))
        0))


(defun f (l) ; Appends the first element to the end of the list and calls f2
    (f2 (append l (list (car l)))))

(defun read-pairs (n) 
  (if (eq n 0) ()
    (cons (list (read *standard-input*) (read *standard-input*)) (read-pairs (- n 1 )))))

(defun solve-case ()
  (f (read-pairs (read))))

(princ (solve-case))