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)

function Main(input){
  input = input.split("\n");
  inputStr = input[0].split(" ");
  const N = Number.parseInt(inputStr[0]);
  inputStr = input[1].split(" ");
  const B = inputStr.map(inputStr => Number.parseInt(inputStr));
  //格納用配列
  var ans = 0;
  ans += B[0];
  for(var i=1 ; i<N-1 ; i++ ){
    if(B[i]>B[i-1]){
      ans += B[i-1];
    } else {
      ans += B[i];
    }
  }
  ans += B[N-2];
  
  //結果出力
  console.log(ans);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));