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>
#include <cmath>
#include <cstdlib>
#include <bitset>
#include<vector>
#include<utility>
#include<fstream>
#include<queue>
#include <iomanip>
using namespace std;
typedef long long ll;
#define rep(i,k) for(i=0;i<k;i++)
#define P pair<ll,ll>
int s[2005];
int t[2005],u[200];

ll i, a, b, c,n,m, z=0;
int day[1005], pos[1005];
vector<int> ss;
vector<int> tt[100000];
int main() {
	cin >> n;
	a = 100005;
	rep(i, n - 1) {
		cin >> b;
		z += min(a, b);
		a = b;
	}
	z += b;
	cout << z;
}