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.ArrayList;
import java.util.Scanner;

public class Main {
    static int N;
    static int[] b;

    private static void init() {
        Scanner scanner = new Scanner(System.in);
        N = scanner.nextInt();
        b = new int[N - 1];
        for(int i = 0; i < N - 1; i++) {
            b[i] = scanner.nextInt();
        }
        scanner.close();
    }


    public static void main(String args[]) {
        init();

        ArrayList<Integer> l = new ArrayList<>();
        l.add(b[0]);
        l.add(b[N - 2]);

        int min = Integer.MAX_VALUE;
        for(int i = 1; i < N - 1; i++) {
            min = Math.min(b[i], b[i - 1]);
            l.add(min);
        }

        int ans = 0;
        for(int i: l) {
            ans += i;
        }
        System.out.println(ans);
    }
}