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.Linq;
using System.Collections.Generic;

public class Program {
  public static void Main() {
    int N = int.Parse(Console.ReadLine().Trim());
    List<int> B = Console.ReadLine().Trim().Split(' ').Select(x => int.Parse(x)).ToList();    
    
    List<int> A = new List<int>();
    A.Add(B[0]);
    for(var i = 0; i < B.Count() - 1; i++) {
      A.Add(Math.Min(B[i], B[i + 1]));
    }
    A.Add(B[B.Count - 1]);
    Console.WriteLine(A.Sum());
  }
}