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: Runtime Error)

import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    int n = sc.nextInt(); 
    //AはBより場所が1つ多い
    int a[] =new int[n+1];
    int b[] =new int[n];
    int ans = 0;
//配列B格納
    for(int i=0; i<b.length; ++i){
      b[i] = sc.nextInt();
    }
//とりあえずAにBを格納
   for(int i=0; i<b.length; ++i){
		    a[i]=b[i];
		}
    //AのラストにBのラストを格納
		a[(n+1)]=b[n];
    //Aに入ってるやつより、直前のBのほうが小さかったら更新
		for(int i=1; i<a.length; ++i){
		    if(a[i]>b[(i-1)]){
		        a[i]=b[(i-1)];
		    }
		}
    
    
    for(int i = 0; i < a.length; ++i){
      ans = ans + a[i];
    }

    System.out.println(ans);
  }
}