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;

void fnInput(vector<int>& rvnSeqB)
{
  int nSeqBSiz;
  cin >> nSeqBSiz;
  rvnSeqB.resize(nSeqBSiz - 1);

  for (int& rnSeqB : rvnSeqB)
    cin >> rnSeqB;
}
  
int fnMaxValueGet(const vector<int>& cnrvnSeqB)
{
  vector<int> vnSeqA(cnrvnSeqB.size() + 1, INT_MAX);

  for (int n = 0; n < cnrvnSeqB.size(); n++)
    if (cnrvnSeqB[n] < vnSeqA[n])
      vnSeqA[n + 1] = vnSeqA[n] = cnrvnSeqB[n];
    else
      vnSeqA[n + 1] = cnrvnSeqB[n];

  int nSumSeqA = 0;
  for (int nSeqA : vnSeqA)
    nSumSeqA += nSeqA;

  return nSumSeqA;
}
  
int main()
{
  vector<int> vnSeqB;

  fnInput(vnSeqB);
  cout << fnMaxValueGet(vnSeqB) << endl;

  return 0;
}