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.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] a = new int[N];
		int[] b = new int[N-1];
		int sum = 0;

		for(int i = 0; i<N-1;i++) {
			b[i] = sc.nextInt();
		}
		
		for(int i = 0;i<N-1;i++) {
			a[i] = b[i];
			a[i+1]=b[i];
			

		}
		for(int i = 0;i<N-2;i++) {

			if(b[i+1] > b[i] ) {
				a[i+1] = b[i];
			}
				

		}
		
		for(int i=0;i<N;i++) {
			sum += a[i];
		}
		

		System.out.println(sum);

		sc.close();
	}
}