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;
using System.Windows;
using System.Collections.Generic;
using System.Linq;

class Program
 {
        static void Main(string[] args)
        {
          //入力を受け取る
          int n = int.Parse(Console.ReadLine());
          string[] B = Console.ReadLine().Split(' ');          
          int sum = int.Parse(B[0])+int.Parse(B[n-2]);
          for (int i = 1; i < n-1; i++){
            if(int.Parse(B[i-1]) >= int.Parse(B[i])){
              sum += int.Parse(B[i]);
            }else{
              sum += int.Parse(B[i-1]);
            }
          }
          System.Console.WriteLine(sum);
        }
 }