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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
)

func main() {
	var n int
	fmt.Scan(&n)
	bNums := ScanNums(n-1)
	aNums := make([]int, n)
	aNums[n-1] = bNums[len(bNums)-1]
	for i := n-2; i >= 0; i-- {
		var max int
		if i-1 < 0 || bNums[i] < bNums[i-1] {
			max = bNums[i]
		} else {
			max = bNums[i-1]
		}
		aNums[i] = max
	}

	maxSum := 0
	for _, num := range aNums {
		maxSum += num
	}
	fmt.Println(maxSum)
}

func ScanNums(len int) (nums []int) {
	var num int
	for i := 0; i < len; i++ {
		fmt.Scan(&num)
		nums = append(nums, num)
	}
	return
}