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 Scala (2.11.7) (judge verdict: Wrong Answer)

import java.util.Scanner

object Main extends App {
  val sc = new Scanner(System.in)
  val n = sc.nextInt
  val array = Array.fill(n - 1)(sc.nextInt)
  // 最初の一個と最後の1ko
  val a1 = array(0)
  val an = array(n - 2)
  val ai = if (array.size > 2) {
    array
      .sliding(2)
      .map(b => Math.min(b(0), b(1)))
      .sum
  } else 0

  println(a1 + an + ai)
}