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 JavaScript (node.js v5.12) (judge verdict: Accepted)

'use strict'

const main = input => {
	const args = input.split('\n').map(arg => arg.split(' '))
	const N = parseInt(args[0][0], 10)
	const B = args[1].map(arg => parseInt(arg, 10))
	const A = new Array(N).fill(0)
	let ans = 0

	A[0] = B[0]

	for (let i = 1; i < N - 1; i++) {
		A[i] = Math.min(B[i - 1], B[i])
	}

	A[N - 1] = B[N - 2]

	for (let i = 0; i < N; i++) {
		ans += A[i]
	}

	console.log(ans)
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'))