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<bits/stdc++.h>
using namespace std;
int main(){
   int N,count;
   cin>>N;
   count=0;
   vector<int> A(N),B(N-1);
   for(int i=0;i<N-1;i++){
      cin>>B.at(i);
   }

   A.at(0)=B.at(0);
   A.at(N-1)=B.at(N-2);
   for(int i=1;i<N-1;i++){
      A.at(i)=min(B.at(i-1),B.at(i));
   }
   for(int i=0;i<N;i++){
      count+=A.at(i);
   }
   cout<<count<<endl;
}