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;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using static MyIO;

namespace atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = GetInt();
            int[] B = GetInts(N-1);

            int ans = B[0];

            for(int i = 1; i < N-1; i++)
            {
                if(B[i-1] < B[i])
                {
                    ans += B[i - 1];
                }
                else
                {
                    ans += B[i];
                }
            }
            ans += B[N-2];

            Console.WriteLine(ans);
        }
    }
}


public static class MyIO
{
    private static string[] args = null;
    private static int num = -1;
    private static int used = -1;

    private static string getArg()
    {
        if (used == num)
        {
            args = Console.ReadLine().Split(' ');
            num = args.Length;
            used = 0;
        }
        return args[used++];
    }

    public static int GetInt() => int.Parse(getArg());
    public static long GetLong() => long.Parse(getArg());
    public static double GetDouble() => double.Parse(getArg());
    public static string GetString() => getArg();
    public static char GetChar() => getArg()[0];
    public static int[] GetInts(int N) => Enumerable.Range(0, N).Select(_ => GetInt()).ToArray();
    public static long[] GetLongs(int N) => Enumerable.Range(0, N).Select(_ => GetLong()).ToArray();
    public static double[] GetDoubles(int N) => Enumerable.Range(0, N).Select(_ => GetDouble()).ToArray();
    public static string[] GetStrings(int N) => Enumerable.Range(0, N).Select(_ => GetString()).ToArray();
}