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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<iostream>
using namespace std;
 
int main(){
    int n, ans=0;
    cin >> n;
    int b[n-1],a[n];
    for(int i = 0; i < n -1; i++) cin >> b[i];

    for(int i = 0; i < n; i++){
        if(i == 0){
            a[i] = b[i];
        } else if(i < n -1){
            if(b[i] > a[i-1] && b[i-1] <= b[i]){
                a[i] = a[i-1];
            } else {
                a[i] = b[i];
            }
        }

        if(i == n -1) a[i] = b[i-1];
        ans +=a[i];
    }

    cout << ans << endl;    
    
}