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: Accepted)

import java.util.*;
import java.util.stream.*;

public class Main {
  public static void main(String[] args) {
    Main main = new Main();
    System.out.println(main.solve());
  }

  int n;
  int a[];

  public Main() {
    Scanner sc = new Scanner(System.in);
    try {
      n = sc.nextInt();
      a = IntStream.range(0, n - 1).map(i -> sc.nextInt()).toArray();
    } finally {
      sc.close();
    }
  }

  int solve() {
    int ans = 0;
    for (int i = 0; i < n; i++) ans += calc(i);
    return ans;
  }

  private int calc(int i) {
    if (i == 0) return a[0];
    if (i == n - 1) return a[n - 2];
    return a[i - 1] < a[i] ? a[i - 1] : a[i];
  }
}