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;

class Program
{
    static void Main()
    {
        var n = int.Parse(Console.ReadLine());
        string[] b = Console.ReadLine().Split(' ');

        int[] ans = new int[b.Length + 1];
        for (int i = 0; i < (n - 1); i++)
        {
            if (i == 0)
            {
                ans[i] = int.Parse(b[i]);
                ans[i + 1] = ans[i];
            }
            else
            {
                if (ans[i] < int.Parse(b[i]))
                {
                    ans[i + 1] = int.Parse(b[i]);
                }
                else
                {
                    if (ans[i] >= int.Parse(b[i]))
                    {
                        ans[i] = int.Parse(b[i]);
                        ans[i + 1] = int.Parse(b[i]);
                    }
                    else
                    {
                        ans[i + 1] = ans[i];
                    }
                }
            }
        }
        Console.WriteLine(ans.Sum());
    }
}