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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;

namespace C
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string[] In = Console.ReadLine().Split(' ');
            int[] B = new int[n - 1];
            for(int i=0; i < n - 1; i++)
            {
                B[i] = int.Parse(In[i]);
            }
            long sum = B[0];
            for(int i=0; i < n - 2; i++)
            {
                sum += (int)Math.Min(B[i], B[i + 1]);
            }
            sum += B[n - 2];
            Console.WriteLine(sum);
        }
    }
}