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: Accepted)

<?php
    $num = (int)fgets(STDIN);
    $cond = explode(" ", fgets(STDIN));

$ans = 0;

for($k=0; $k<$num; $k++){
  if($k < $num-1){
      $cond[$k] = (int)$cond[$k];
  }
  if($k <= count($cond)-1){
    if($k === 0){   
      $ans += $cond[0];
    }elseif($cond[$k] > $cond[$k-1]){
      $ans += $cond[$k-1];
    }else{
      $ans += $cond[$k];
    }
  }else{
    $ans += $cond[$k-1];
  }
}

echo $ans;