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 Kotlin (1.0.0) (judge verdict: Accepted)

import java.util.*

fun main(args: Array<String>) {

    val n = Integer.parseInt(readNext())

    val a = readNext().split(" ").map { Integer.parseInt(it) }
    var list = mutableListOf<Int>()
    var result = 0
    var tmp = 0
    for (i in 0..n - 1) {
        list.add(0)
    }
    var pre = 0;
    for (i in 0..a.size - 1) {
        val n = a[i]
        val s = list[i]
        val t = list[i + 1]
        if(i == 0) {
            list[i] = n
            if (i == a.size - 1) {
                list[i + 1] = n
            }
            pre = n
            continue
        }
        var tmp = Math.max(Math.abs(n), Math.abs(s))
        if (pre >= tmp) {
            list[i] = tmp
        } else {
            list[i] = pre
        }
        pre = n
        if (i == a.size - 1) {
            list[i + 1] = Math.max(Math.abs(n), Math.abs(t))
        }
    }
    println(list.sum())
}
fun readNext(): String {
    return readLine()!!
}