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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.*;
import java.util.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Collections;
import java.util.Arrays;

public class Main {
	public static void main(final String[] args){
    
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    List<Integer> list = new ArrayList<>();
    int sum = 0;

    for(int i = 0 ; i < n - 1 ; i++){
        list.add(sc.nextInt());
    }

    if(n == 2){
        System.out.println(list.get(0)*2);
        System.exit(0);
    }
    for(int i = 0 ; i < n - 2; i++){
        if(i == 0){
            if(list.get(i) > list.get(i + 1)){
                sum += list.get(i)+list.get(i+1);
            }else{
                sum += list.get(i)*2; 
            }
        }else{
            if(list.get(i) > list.get(i+1)){
                sum += list.get(i+1);
            }else{
                sum += list.get(i);
            }
        }

        if(i == n - 3){
            sum += list.get(i+1);
        }
    }

    System.out.println(sum);
    



    





}
}