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,ans,t;
  
  ans=0;
 
  cin>>n;
vector<int> vec(n-1);
  vector<int> a(n);

 for(int i=0; i<vec.size(); i++){
    cin>>vec.at(i);
   a.at(i)=vec.at(i);
}
  a.at(n-1)=vec.at(n-2);
t=vec.at(0);
  for(int i=0; i<vec.size(); i++){
    
    if(t>=a.at(i)&&t>=a.at(i+1))ans+=a.at(i);

     else{a.at(i+1)=a.at(i);
       ans+=a.at(i);
     
     
     } 
      t=vec.at(i+1);
      }
  
  ans+=a.at(n-2);
  
  cout<<ans<<endl;
  
}