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.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number, i, sum = 0, tmp = -1;
    number = Integer.parseInt(sc.next());
    int[] array_a = new int[number];
    int[] array_b = new int[number-1];
    for(i = 0; i < number-1; i++) {
      array_b[i] = Integer.parseInt(sc.next());
    }
    array_a[0] = array_b[0];
    for(i = 1; i < number-1; i++) {
      array_a[i] = Math.min(array_b[i-1], array_b[i]);
    }
    array_a[i] = array_b[i-1];
    for(i = 0; i < number; i++) {
      sum += array_a[i];
    }
    System.out.println(sum);
  }
}