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

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int mod = (int)1e9 + 7;
        int n = sc.nextInt();
        int[] b = new int[n-1];
        for  (int i = 0; i < n-1; i++) {
            b[i] = sc.nextInt();
        }
        int[] a = new int[n];
        a[0] = b[0];
        int ans = a[0];
        for  (int i = 1; i < n; i++) {
            if (i == n-1) {
                a[i] = b[i-1];
            } else {
                a[i] = Math.min(b[i-1], b[i]);
            }
            ans += a[i];
        }
        System.out.println(ans);
    }

}