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 (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

var sc = bufio.NewScanner(os.Stdin)

func gets() string {
	sc.Scan()
	return sc.Text()
}

func atoi(s string) int {
	i, err := strconv.Atoi(s)
	if err != nil {
		panic(err)
	}
	return i
}

func main() {
	var n int
	fmt.Scan(&n)
	var a []int

	b := strings.Split(gets(), " ")

	// fmt.Println(A)
	// fmt.Println(B)

	a = append(a, atoi(b[0]))

	for i := 1; i < len(b); i++ {
		work := atoi(b[i])
		work2 := atoi(b[i-1])
		if work > work2 {
			a = append(a, work2)
		} else {
			a = append(a, work)
		}
	}
	a = append(a, atoi(b[len(b)-1]))

	sum := 0

	for _, value := range a {
		sum += value
	}

	// fmt.Println(a)
	fmt.Println(sum)
}