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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
class Program
{
  static void Main(string[] args)
  {
    // 入力値を取得
    int n = int.Parse(Console.ReadLine());
    string[] input = Console.ReadLine().Split(' ');
    int[] array = new int[n-1];
    for (int i = 0; i < n-1; i++){
      array[i] = int.Parse(input[i]);
    }
    
    int sum = 0;
    for (int j = 0; j < n-1; j++)
    {
      if (j == 0)
      {
        sum += array[j];
      }
      else
      {
        sum += (array[j] <= array[j-1]) ? array[j] : array[j-1];
      }
    }
    sum += array[n-2];
    Console.WriteLine(sum);
  }
}