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)
	bs := make([]int, n-1)
	r := 0
	for i := range bs {
		fmt.Scan(&bs[i])
	}
	if n == 2 {
		fmt.Println(bs[0] * 2)
	} else {
		r += bs[0]
		r += bs[n-2]
		for i := 1; i < n-1; i++ {
			r += min01(bs[i-1], bs[i])
		}
		fmt.Println(r)
	}
}

func min01(a, b int) int {
	if a < b {
		return a
	} else {
		return b
	}
}