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;
class Program
{
  static void Main()
  {
    int N = int.Parse(Console.ReadLine());
    string[] B = Console.ReadLine().Split(' ');
    int sum = 0;
    
    for (int i = 0; i < N; i++)
    {
      int A = 0;
      if (i == 0){
        A = int.Parse(B[i]);
      }
      else if (i == N - 1){
        A = int.Parse(B[i - 1]);
      }
      else{
        A = Math.Min(int.Parse(B[i - 1]), int.Parse(B[i]));
      }
      sum += A;
    }
    
    Console.WriteLine(sum);
  }
}