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>
#define Inf 0x3f3f3f3f
#define rg register
using namespace std;
typedef long long ll;
inline ll min(ll x, ll y) { return x < y ? x : y; }
inline ll max(ll x, ll y) { return x > y ? x : y; }
const int Maxn = 1e5 + 5;
inline ll read()
{
	rg ll res = 0, sign = 1;
	rg char ch = getchar();
	while (!isdigit(ch))
	{
		if (ch == '-')
			sign = -1;
		ch = getchar();
	}
	do
	{
		res = (res << 3) + (res << 1) + (ch ^ 48);
		ch = getchar();
	} while (isdigit(ch));
	return res * sign;
}
int n, b[Maxn];
int ans;
int main()
{
	cin >> n;
	for (int i = 1; i < n; i++)
		b[i] = read();
	for (int i = 2; i < n; i++)
		ans += min(b[i], b[i - 1]);
	ans += b[1] + b[n - 1];
	cout << ans << endl;
	return 0;
}