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 void Main(string[] args)
    {
        int N = int.Parse(Console.ReadLine());
        int[] B = new int[N];
        var input = Console.ReadLine().Split();
        int[] A = new int[N];
        for (int i = 0; i < N-1; i++)
        {
            B[i] = int.Parse(input[i]);
        }
        int sum = 0;
        for (int i = 0; i < N; i++)
        {
            if (i == 0) { A[0] = B[0]; }
            else if (i == N - 1) { A[i] = B[i - 1]; }
            else { A[i] = Math.Min(B[i],B[i-1]); }
            sum += A[i];
        }
        Console.WriteLine(sum);
    }
}