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 <iostream>
#include <string>
#include<algorithm>
using namespace std;

int main()
{   //数N
	int N;
	cin >> N;

	int A[100] = { 0 };
	int B[100];

	for (int i = 0; i < N - 1; i++) {
		cin >> B[i];
	}

	for (int i = 0; i < N; i++) {
		if (i == 0) {
			A[i] = B[i];
		}
		else if (i == N - 1) {
			A[i] = B[i-1];
		}
		else {
			A[i] = min(B[i], B[i - 1]);
		}
	}

	int sum = 0;
	for (int i = 0; i < N; i++) {
		sum = sum + A[i];
	}
	cout << sum << endl;
	

	return 0;
}