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.

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.

Constraints

• All values in input are integers.
• $2 \leq N \leq 100$
• $0 \leq B_i \leq 10^5$

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

见题面 Input 部分

见题面 Output 部分