Problem:
Score : 300 points

Problem Statement

There is an integer sequence A of length N whose values are unknown.

Given is an integer sequence B of length N-1 which is known to satisfy the following:

B_i \geq \max(A_i, A_{i+1})

Find the maximum possible sum of the elements of A.

Constraints

All values in input are integers.

2 \leq N \leq 100

0 \leq B_i \leq 10^5

Input

Input is given from Standard Input in the following format:

N
B_1 B_2 ... B_{N-1}

Output

Print the maximum possible sum of the elements of A.

Sample Input 1

3
2 5

Sample Output 1

9

A can be, for example, ( 2 , 1 , 5 ), ( -1 , -2 , -3 ), or ( 2 , 2 , 5 ). Among those candidates, A = ( 2 , 2 , 5 ) has the maximum possible sum.

Sample Input 2

2
3

Sample Output 2

6

Sample Input 3

6
0 153 10 10 23

Sample Output 3

53

Solution in Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

(let* ((n (read))
       (lst (loop :repeat (1- n) :collect (read)))
       (lst-a (cons (car lst) lst))
       (lst-b (concatenate 'list lst (last lst)))
       (lst-t (concatenate 'list '(nil) (mapcar #'<= lst (cdr lst)) '(T))))
  (princ (reduce #'+ (mapcar (lambda (a b c)
                               (if a b c)) lst-t lst-a lst-b) )))