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;

class Program
{
	static void Main(string[] args)
	{
		int N = int.Parse(Console.ReadLine());
		var B = Console.ReadLine().Split(' ');
		var Bl = new List<int>();
		foreach (var Bs in B) {
			Bl.Add(int.Parse(Bs));
		}
		var Bn = Bl.ToArray();
		int ans = 0;
		int An =0;
		
		
		for (int i = 0; i < N; i++) {
			if(i < Bn.Length){
				An = Bn[i];
			}else{
				An = Bn[i-1];
			}
			if (i - 1 != -1) {
				if (Bn[i - 1] < An)
					An = Bn[i - 1];
			}
			ans += An;
		}
		Console.Write(ans);
	}
}