(defvar c)
(defvar rin)
(defvar rout)
(defvar temp)
(setq c (parse-integer (read-line)))
(setq temp (read-from-string (concatenate 'string "(" (read-line) ")")))
(setq rin (nth 0 temp))
(setq rout (nth 1 temp))

(defvar han)
(setq han (/ (- rout rin) 2))
(format t "~f~%" (* han han 3.1415926535 (* 2 3.1415926535 (/ (+ rout rin) 2)) c))