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;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        static long ReadLong()
        {
            return long.Parse(Console.ReadLine());
        }

        static long[] ReadLongs()
        {
            return Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
        }

        static double ReadDouble()
        {
            return double.Parse(Console.ReadLine());
        }

        static double[] ReadDoubles()
        {
            return Console.ReadLine().Split(' ').Select(double.Parse).ToArray();
        }

        static string ReadString()
        {
            return Console.ReadLine();
        }

        static string[] ReadStringSplit()
        {
            return Console.ReadLine().Split(' ');
        }

        static void A()
        {
            long N = ReadLong();
            Console.WriteLine(N * N * N);
        }

        static void B()
        {
            long N = ReadLong();
            long[] A = ReadLongs();
            long[] B = ReadLongs();
            long[] C = ReadLongs();
            long ans = 0;
            long prev = -100;
            for (int i = 0; i < N; i++)
            {
                ans += B[A[i] - 1];
                if (prev == A[i] - 1)
                {
                    ans += C[prev - 1];
                }
                prev = A[i];
            }
            Console.WriteLine(ans);
        }

        static void C()
        {
            long N = ReadLong();
            long[] B = ReadLongs();
            long ans = 0;
            for (int i = 0; i < N; i++)
            {
                if (i == 0)
                {
                    ans += B[0];
                }
                else if (i == N - 1)
                {
                    ans += B[N - 2];
                }
                else
                {
                    ans += Math.Min(B[i - 1], B[i]);
                }
            }
            Console.WriteLine(ans);
        }

        static void D()
        {

        }

        static void Main(string[] args)
        {
            //A();
            //B();
            C();
            //D();
        }
    }
}