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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int b[] = new int[n - 1];
		long ans = 0;
		int pre = 0;
		int aft = 0;
		for (int i = 0; i < n - 1; ++i)
		b[i] = sc.nextInt();
		sc.close();
		for(int i = 0; i < n - 1; ++i){
			int tmp = b[i];
			if(i != n - 2)aft = b[i + 1];
			if(i == 0){
				tmp <<= 1;
			}else if (i != n - 2){
				if(pre < tmp && tmp > aft)
				tmp = Math.max(pre, aft);
			}
			ans += tmp;
			pre = tmp;
		}
		System.out.println(ans);
	}
}