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;
typedef unsigned long long ll;
const int maxn = 1e3+5;
int main()
{
    int b[maxn], a[maxn] = {0};
    int n, sum = 0;
    cin >> n;
    for (int i = 0; i < n - 1; i++)
        cin >> b[i];
    for (int i = 0; i < n; i++){
        if (b[i+1] < b[i])
           a[i+1] = b[i+1];
        else
           a[i+1] = b[i];
    }
    a[0] = b[0];
    for (int i = 0; i < n; i++)
    sum += a[i];
    cout << sum << endl;
    return 0; 
}