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;

namespace testes
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int[] B = new int[N - 1];
            string[] str = Console.ReadLine().Split(' ');
            for (int i = 0; i < N-1; i++) B[i] = int.Parse(str[i]);

            int[] A = new int[N];
            A[0] = B[0];
            for(int i = 1; i < N - 1; i++)
            {
                A[i] = Math.Min(B[i], B[i - 1]);
            }
            A[N - 1] = B[N - 2];
            int ans = 0;
            for (int i = 0; i < N; i++) ans += A[i];
            Console.WriteLine(ans);
        }
    }

}

/*
int a, b, c;
a = int.Parse(Console.ReadLine()); //標準入力
string[] str = Console.ReadLine().Split(' ');//2つ以上のスペース区切り入力の取得
b = int.Parse(str[0]);  //数値で受け取りたい場合は変換する
c = int.Parse(str[1]);
Console.Write("改行なし a = {0} b = {1} c = {2}", a, b, c)//改行なし出力
Console.WriteLine("改行あり a = {0} b = {1} c = {2}", a, b, c);//改行付き出力

string[] str = Console.ReadLine().Split(' ');
int[] a = new int[N];
for(int i = 0; i < N; i++) a[i] = int.Parse(str[i]);
 */