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: Runtime Error)

#include <bits/stdc++.h>
using namespace std;
 
int main() {
    int N;
    vector<int> A(N);
    vector<int> B(N-1);

    cin >> N;
    for(int i = 0 ; i < N-1 ; i++){
        cin >> B.at(i);
    }
     if(B.at(0) > B.at(1)) A.at(0)=B.at(1);
       else A.at(0)=B.at(0);
       
   for(int i = 0 ; i <N-2; i++){
       if(B.at(i) > B.at(i+1)) A.at(i+1)=B.at(i+1);
       else A.at(i+1)=B.at(i);
   }

   A.at(N)=B.at(N-1);

int sum = 0;
   for(int i=0 ; i<N ;i++) sum += A.at(i);

   cout << sum;
return 0;


}