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: Accepted)

#include<iostream>
#include<algorithm>
#include<vector>
#define ll long long
using namespace std;

int main(){
    int n;
    ll tmp,sum;
    vector<ll> a,b;

    cin>>n;
    for(int i=0; i<n-1; i++){
        cin>>tmp;
        b.push_back(tmp);
    }
    a.push_back(b[0]);
    for(int i=1; i<n-1; i++){
        a.push_back(min(b[i-1],b[i]));
    }
    a.push_back(b[n-2]);

    sum=0;
    for(int i=0; i<n; i++){
        //cout<<"a : "<<a[i]<<endl;
        sum+=a[i];
    }
    cout<<sum<<endl;
    return 0;
}