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.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ClassLibrary1
{
    public class ListNode
    {
        public int val;
        public ListNode next;
        public ListNode(int x) { val = x; }
    }


    public class Class1
    {
        static int[][] mtx ;
        static List<int>[] tm;
        static int n;
        static int[] results;
        static List<string> cons = new List<string>();
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string[] s1 = Console.ReadLine().Split(' ');

            int[] n1 = new int[n-1];

            for (int i = 0; i < n - 1; i++)
            {
                n1[i] = int.Parse(s1[i]);
            }

            if (n == 2)
            {
                Console.WriteLine(n1[0]*2);
                return;
            }

            if (n==3)
            {
                var sum = n1[0] + n1[1] + Math.Min(n1[0], n1[1]);
                Console.WriteLine(sum);
                return;
            }


            var score = 0;
            score += n1[0];
            score += n1[n - 2];

            for (int i = 0; i < n-2; i++)
            {
                var min = Math.Min(n1[i], n1[i + 1]);
                score += min;
            }

            Console.WriteLine(score);
        }

 

    }

}