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 {
    	
    private final static Scanner sc = new Scanner(System.in);
    	
    public static void main(String[] arg) {
    	int N = sc.nextInt();
    	int b = sc.nextInt();
      	int sum = 2 * b;
      	int b2;
      	for(int i = 0; i < N-2; i++) {
        	b2 = sc.nextInt();
          	if(b2 < b) {
              sum = sum - b + b2;
            }
          	b = b2;
          	sum += b;
        }
      	System.out.println(sum);
          
   	}
}