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>
    #include<cmath>
    using namespace std;

    int main(){
        int n;
        int b[200];

        cin >> n;
        for(int i = 1; i <= n-1; i++) cin >> b[i];
        // cout << endl ;

        int ans = 0;
        int tmp = 0;
        for(int i = n-1;; i--){
            if(b[i] <= b[i+1] || i == n-1){
                ans += b[i];
                tmp = b[i];
                // cout << "b[" << i << "] is " << b[i] << " b[" << i+1 << "] is " << b[i+1] << endl;
                // cout << "if " <<tmp << endl;
            } else {
                ans += b[i+1];
                tmp = b[i+1];
                // cout <<"else " << tmp << endl;

        }
        if(i == 1){  
            ans += tmp;
            // cout << tmp << endl;
            break;
        }
        }
        cout << ans << endl;
    }