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;

class Program
{
    static void Main(string[] args)
    {
        long N = GetInputLong();

        int[] B = GetInputsInt();

        long sum = 0;

        sum += B[B.Length - 1];
        for (int i = B.Length-1; i >0 ; i--)
        {
            sum += Math.Min(B[i], B[i - 1]);
        }
        sum += B[0];

        Console.WriteLine(sum);

        Console.ReadKey();
    }



    public static int GetInputInt()
    {
        return int.Parse(Console.ReadLine());
    }
    public static int[] GetInputsInt()
    {
        return Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
    }
    public static List<int> GetInputsIntList()
    {
        return Console.ReadLine().Split(' ').Select(int.Parse).ToList();
    }
    public static List<float> GetInputsFloatList()
    {
        return Console.ReadLine().Split(' ').Select(float.Parse).ToList();
    }

    public static long GetInputLong()
    {
        return long.Parse(Console.ReadLine());
    }
    public static long[] GetInputsLong()
    {
        return Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
    }

}