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 PHP (5.6.30) (judge verdict: Accepted)

<?php
# 数値の入力
fscanf(STDIN, "%d", $data1);
$data2 = trim(fgets(STDIN));
$a = explode(" ", $data2);

$anser = $a[$data1-2];

for($i=0; $i<$data1-1; $i++){
    if($i!=0){
        if($a[$i]>=$a[$i-1]){
            $anser += $a[$i-1];
        }else{
            $anser += $a[$i];
        }
    }else{
        $anser += $a[$i];
    }
}

echo $anser;
?>