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;

class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("3");
            WillReturn.Add("2 5");
            //9
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("2");
            WillReturn.Add("3");
            //6
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("6");
            WillReturn.Add("0 153 10 10 23");
            //53
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();

        int[] BArr = InputList[1].Split(' ').Select(X => int.Parse(X)).ToArray();
        int UB = BArr.GetUpperBound(0);
        var AList = new List<int>();

        long Answer = 0;
        for (int I = 0; I <= UB + 1; I++) {
            int Ind1 = I - 1;
            int Ind2 = I;

            var Kouho = new List<int>();
            if (Ind1 >= 0) {
                Kouho.Add(BArr[Ind1]);
            }
            if (Ind2 <= UB) {
                Kouho.Add(BArr[Ind2]);
            }
            Answer += Kouho.Min();
        }
        Console.WriteLine(Answer);
    }
}