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;
#define MOD 1000000007
#define MOD2 998244353
double PHI = 1.6180339;
#define endl "\n"    
typedef long long ll;
#define int long long
//#define int unsigned long long

int32_t main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int n;
    cin>>n;
    int arr[n+10];
    for(int i=1;i<=n-1;i++)
    cin>>arr[i];
    arr[n]=arr[n-1];

    vector<int>v;

    int y=min(arr[1],arr[2]);
    v.push_back(y);

    for(int i=2;i<=n;i++)
    {
        int x=min(arr[i-1],arr[i]);
        v.push_back(x);
    }

    int res=0;
    for(int i=0;i<v.size();i++)
    {
         res+=v[i];
    }
    cout<<res<<endl;




    
}