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"
)

func main() {
	var N int
	fmt.Scanln(&N)

	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	b := make([]int, N-1)
	for i := range b {
		sc.Scan()
		b[i], _ = strconv.Atoi(sc.Text())
	}

	ans := b[0]
	for i := 0; i < N-2; i++ {
		if b[i] <= b[i+1] {
			ans += b[i]
		} else {
			ans += b[i+1]
		}
	}
	ans += b[N-2]
	fmt.Println(ans)
}