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: Wrong Answer)

import java.util.*;

public class Main {

  public static void main (String[] args) {

    Scanner sc = new Scanner(System.in);

    int N = sc.nextInt();
    int[] B = new int[N];

    for(int i = 1; i < N; i++) {
      B[i] = sc.nextInt();
    }

    sc.close();

    int[] A = new int[N+1];
    
    A[N] = B[N-1];

    for (int i = N-1; 1 < i; i--) {
      if (B[i-1] <= B[i]) {
        A[i] = B[i-1];
      } else {
        if (A[i+1] == B[i]) {
          A[i] = B[i];
        } else {
          A[i] = B[i-1];
        }
      }
    }

    A[1] = B[1];

    int max = 0;

    for (int i = 1; i < N+1; i++) {
      max += A[i];
    }

    System.out.println(max);

  }

}