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

class Program
{
    static void Main(string[] args)
    {
        // 入力
        var n = long.Parse(Console.ReadLine());
        long[] numbers = Console.ReadLine().Split().Select(long.Parse).ToArray();


        long[] tmp = new long[n];
        tmp[0] = numbers[0];
        for (int i = 1; i < n; i++)
        {
            if (tmp[i-1] > numbers[i-1])
            {
                tmp[i-1] = numbers[i-1];
            }
            tmp[i] = Math.Max(numbers[i - 1], tmp[i - 1]);
        }


        long ans = 0;
        for (int i = 0; i < n; i++)
        {
            ans += tmp[i];
        }
        Console.WriteLine(ans);

    }
}