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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
//error_reporting(0);
$N = trim(fgets(STDIN));
//list($A,$B) =  explode(" ",trim(fgets(STDIN)));
$B = explode(" ",trim(fgets(STDIN)));

$A[0]=$B[0];
for($i=1;$i<$N-2;$i++) {
  $A[$i]=min($B[$i],$B[$i-1]);
}
$A[$N-1]=$B[$N-2];
printf("%d\n",array_sum($A));