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: Wrong Answer)

package main

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

func toI(ss []string) []int {
	ret := make([]int, 0, len(ss))
	for _, s := range ss {
		n, _ := strconv.Atoi(strings.TrimSpace(s))
		ret = append(ret, n)
	}
	return ret
}

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

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

	reader := bufio.NewReader(os.Stdin)

	A, _ := reader.ReadString('\n')

	a := toI(strings.Split(A, " "))

	var sum int64
	sum = int64(a[len(a)-1])
	for i := len(a) - 1; i > 0; i-- {
		sum += int64(min(a[i], a[i-1]))
	}
	fmt.Println(sum)
}