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)

fun main(args : Array<String>) {
  val n = readLine()
  val b =  readLine()!!.split(" ").map{ it.toInt() }
  val a = Array(b.size + 1, {0})
  a[0] = b[0]
  for(i in 1 until b.size){
    a[i] = b[i - 1]
    if(b[i] < a[i]){
      a[i] = b[i]
    }
  }
  a[a.size-1] = b[b.size-1]
  var sum=0
  for(i in 0 until a.size){
    sum+=a[i]
  }
  println(sum)
}