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;

public class Hello{
    public static void Main(){
        var n = Console.ReadLine();
        var b = ReadList();
        var a = new int[b.Count + 1];
        
        for(int i = 0; i <= b.Count; i++){
            a[i] = (int)1e5;
        }
        
        for(int i = 0; i < b.Count; i++){
            if(a[i] > b[i]){
                a[i] = b[i];
            }
            
            if(a[i + 1] > b[i]){
                a[i + 1] = b[i];
            }
        }
        
        long sum = 0;
        
        for(int i = 0; i <= b.Count; i++){
            sum += a[i];
        }
        
        Console.WriteLine(sum);
    }
    
    public static List<int> ReadList(){
        var a_text = Console.ReadLine().Split(' ');
        return a_text.Select(x => int.Parse(x)).ToList();
    }
}