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: Wrong Answer)

using System;
using System.Linq;

namespace abc140_c
{
    static class Program
    {
        static void Main(string[] args)
        {
            var n = Console.ReadLine().ToInteger();
            // var a = new int[n];
            var b = Console.ReadLine().ToIntArray();

            // b[i] >= Math.Max(a[i], a[i + 1]);
            var ans = 0L;
            // a[0] = b[0];
            for (int i = 0; i < b.Length; i++)
            {
                if (i + 1 < b.Length && b[i] > b[i + 1])
                {
                    // ただし、i > i + 1 の時はi + 1を入れる
                    // a[i + 1] = b[i + 1];
                    ans += b[i + 1];
                }
                else
                {
                    // 基本的にはbの値を入れる
                    // a[i + 1] = b[i];
                    ans += b[i];
                }
            }

            // Console.WriteLine($"{string.Join(" ", a)}");
            Console.WriteLine($"{ans}");
        }

        static int ToInteger(this string s)
        {
            return int.Parse(s);
        }

        static int[] ToIntArray(this string s, char separator = ' ')
        {
            return s.Split(separator).Select(m => m.ToInteger()).ToArray();
        }
    }
}