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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main{
    
    public static void main (String[] args){
        
        Scanner sc = new Scanner (System.in);
        
        int N = sc.nextInt();
        int[] listB = new int [N-1];
        int [] listA = new int [N];
        
        for (int index=0; index<N-1; index++){
            listB[index]=sc.nextInt();
        }
        
        int lastNum = 0;
        
        for (int index=0; index<N-1; index++){
            int num = listB[index];
            listA[index]=num;
            if (index!=0){
                if (listA[index]>lastNum){
                    listA[index]=lastNum;
                }
            }
            lastNum = num;
        }
        
        listA[N-1]=listB[N-2];
        
        int total = 0;
        
        for (int index=0; index<N; index++){
            total+=listA[index];
        }
        
        System.out.println(total);
    }
}