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;

int main() {
    int n;
    cin>>n;
    int b[n-1];
    for(int i=0;i<n;i++) cin>>b[i];
    int a[n];
  	a[0]=b[0];
    for(int i=1;i<n-1;i++) {
        a[i]=min(b[i], b[i-1]);
    }
    a[n-1]=max(b[n-2], b[n-3]);
  
  	int sum=0;
  	for(int i=0;i<n;i++) {
      sum+=a[i];
    }
  	cout<<sum<<endl;
}