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.lang.Math

fun main(args: Array<String>)
{
    val (n) = readInts()
    val b = readIntArr()

    var sum = b[0] + b[n-2]

    for (i in 0..n-3) {
        sum += if (b[i] < b[i+1]) b[i] else b[i+1]
    }

    println(sum)
}

fun readInts(): List<Int> = readLine()!!.split(" ").map(String::toInt)
fun readLongs(): List<Long> = readLine()!!.split(" ").map(String::toLong)

fun readIntArr(): IntArray = readLine()!!.split(" ").map(String::toInt).toIntArray()
fun readLongArr(): LongArray = readLine()!!.split(" ").map(String::toLong).toLongArray()

fun readIntArrS(): IntArray = readLine()!!.split(" ").map(String::toInt).toIntArray().sortedArray()
fun readLongArrS(): LongArray = readLine()!!.split(" ").map(String::toLong).toLongArray().sortedArray()

fun readIntArrSD(): IntArray = readLine()!!.split(" ").map(String::toInt).toIntArray().sortedArrayDescending()
fun readLongArrSD(): LongArray = readLine()!!.split(" ").map(String::toLong).toLongArray().sortedArrayDescending()

fun readString() = readLine()!!