(define n (string->number (read-line)))
(define v (list->vector(map string->number (string-split (read-line) " ")))) 
(define (calc-max i a1 a2)
        (cond
          ((eq? i 3) (max
                      a1 
                      (+ (vector-ref v (+ (- n i) 2)) a2)))
          (else (calc-max 
                  (- i 1)
                  (max
                    a1 
                    (+ (vector-ref v (+ (- n i) 2)) a2))
                  a1))))
(define v0 (vector-ref v 0))                  
(print (cond ((eq? n 1) v0)
              ((eq? n 2) (max v0 (vector-ref v 1)))
              (else 
                (calc-max n 
                          (max v0 (vector-ref v 1))        
                          v0))))