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 JavaScript (node.js v5.12) (judge verdict: Accepted)

"use strict"

function Main(input) {
  input = input.trim().split('\n');
  const N = Number(input[0].trim());
  const B = input[1].trim().split(' ').map(Number);

  let cnt = N-2;
  let ret = B[0] + B[cnt];
  for(let i=0; i<cnt; i++){
    ret += Math.min(B[i], B[i+1])
  }
  console.log(ret);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));