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 <bits/stdc++.h>
using namespace std;
int main()
{

    int n,len;
    long long int val=0;
    vector<long long int>vec,vec_1;
    cin>>len;
    for(int i=0;i<len-1;i++)
    {
        cin>>n;
        vec.push_back(n);
    }
    for(int u=0;u<len-1;u++)
    {
        if(u==0)
        {
            vec_1.push_back(min(vec[u],vec[u+1]));
            vec_1.push_back(min(vec[u],vec[u+1]));
        }
        else
        {
            vec_1.push_back(min(vec[u],vec[u+1]));
        }
    }
    for(int i=0;i<vec_1.size();i++)
       val+=vec_1[i];
    cout<<val<<endl;
    return 0;
}