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.Diagnostics;
using System.IO;
using System.Text;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args) {
#if DEBUG
        //MyDebugger.MakeTestCase("../TextFile2.txt");
        MyDebugger.Test(process, "../TextFile1.txt");
#else
        object ret = process(new StreamReader(Console.OpenStandardInput()));
        Console.WriteLine(ret);
#endif
    }

    static object process(TextReader input) {
        int n = int.Parse(input.ReadLine());
        int[] bb = ToIntArray(input.ReadLine(), n-1);

        int[] aa = new int[n];

        for(int i=0; i<n; i++) {
            int b1 = i==0 ? int.MaxValue : bb[i-1];
            int b2 = i==n-1 ? int.MaxValue : bb[i];

            aa[i] = Math.Min(b1, b2);
        }

        long count = aa.Sum();
        return count;
    }

    static int[] ToIntArray(string strs, int n) {
        int[] ret = new int[n];
        var spl =strs.Split(' ');
        for (int i = 0; i < n; i++) ret[i] = int.Parse(spl[i]);
        return ret;
    }
}