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.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    
    int n = sc.nextInt();

    ArrayList<Integer> a = new ArrayList<Integer>(n);
    ArrayList<Integer> b = new ArrayList<Integer>(n-1);

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

    int p = 0;
    //処理
    for (int i=0 ; i<n-1 ; i++){
        if(i == 0){
            a.set(i, b.get(i));
        }else{
            if(b.get(i) < b.get(i-1)){
                a.set(i, b.get(i));
            }
        }
        a.set(i+1, b.get(i));
        p += (int)a.get(i);
    }
    System.out.println(p+(int)a.get(n-1));
  }
}