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 min3(a,b,c) min(a,min(b,c))
#define max3(a,b,c) max(a,max(b,c))
#define watch(x) cout<<"->"<<#x<<" : "<<x<<endl;
signed main()
{
	//freopen("","r",stdin);
	//freopen("","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	int n;
	cin>>n;
	int b[n-1];
	for(int i=0;i<n-1;i++)cin>>b[i];
	int a[n];
	for(int i=0;i<n-1;i+=1)a[i]=b[i],a[i+1]=b[i];
	for(int i=0;i<n-1;i++)
	{
		if(max(a[i],a[i+1])>b[i])
		{
			if(a[i+1]==max(a[i],a[i+1]))
				a[i+1]=b[i];
			else
				a[i]=b[i];
		}
	}
	int res = 0;
	for(int val : a)res+=val;
	cout<<res<<endl;
	return 0;	
}