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.Scanner;

class Main {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int n = s.nextInt();
		int a[] = new int[n-1];
		for(int i=0;i<n-1;i++) {
			a[i] = s.nextInt();
		}
		int ans[] = new int[n];
		
		for(int i=0;i<n;i++) {
			ans[i] = Integer.MAX_VALUE;
		}
		int k=a.length-1;
		for(int i=n-1;i>=1;i--) {
			ans[i] = Math.min(ans[i], a[k]);
			ans[i-1] = a[k];
			k--;
		}
		int sum=0;
		for(int i:ans) {
			sum+=i;
		}
		System.out.println(sum);
		
	}
}