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;
#define x_ real()
#define y_ imag()
#define cross(a, b) (conj(a)*(b)).imag()
#define dot(a, b) (conj(a)*(b)).real()
#define PI acos(-1)
#define F first
#define S second
#define fastIO ios_base::sync_with_stdio(false), cin.tie(NULL)
#define fileIO freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout)
#define ordered_set tree<int, null_type,less_equal<int>, rb_tree_tag,tree_order_statistics_node_update>
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef complex<ld> point;
typedef tuple<int, int, int> line;
typedef vector<point> polygon;
typedef pair<double, double> pd;
//pair<int, int> dirs[] = { {1, 2}, {-1, 2}, {2, 1}, {2, -1}, {-2, 1}, {-2, -1}, {1, -2}, {-1, -2} };
const ll mod = 1e9 + 7;
const ll N = 2e5 + 7;


int main() {
	fastIO;
	ll n;
	cin >> n;
	int b[n-1];
	for (int i = 0; i < n-1; i++)
		cin >> b[i];

	int ans = 0;
	for (int i = 0; i < n-1; i++) {
		if (i) {
			ans += min(b[i-1], b[i]);
		}
		else {
			ans += b[i];
		}
	}
	ans += b[n-2];
	cout << ans;

}