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){
  var N = input.split("\n")[0];
  var B = input.split("\n")[1].split(" ");


  var count = 0;
  for(i=0;i<=(N-2);i++){
    B[i] = parseInt(B[i],10);
    if(i===0){
      count += 2*B[i];
    }else{
      if(B[i-1]>B[i]){
        count -= B[i-1];
        count += 2*B[i];
      }else{
        count += B[i];
      }
    }
  }
  console.log(count);
}  

Main(require("fs").readFileSync("/dev/stdin", "utf8"));