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<cstdio>
#include<string>
#include<cmath>
#include<algorithm>
#include<vector>
#include<queue>
#include<stack>
using namespace std;
#define rep(i,ra,re) for((i)=ra;(i)<(re);(i)++)
#define _rep(i,ra,re) for((i)=ra;(i)>(re);(i)--)
#define rep_(i,ra,re) for((i)=ra;(i)<=(re);(i)++)
#define _rep_(i,ra,re) for((i)=ra;(i)>=(re);(i)--)
#define put(n) cout << n << " "; 
#define puts(n) cout << n << endl;
#define pu(n) cout << n;
#define mod 1000000007
int i,j,k,l;
static const int MAX_N=10e5;
int B[MAX_N];
int main(void){
	int N;cin >> N;
	long ans=0;rep(i,0,N-1){
		cin >> B[i];}
	rep(i,0,N-2){
		if(B[i]<B[i+1]){
			ans+=B[i];
		}else{
			ans+=B[i+1];
		}
	}
	ans+=(B[N-2]+B[0]);
	puts(ans);
	
	
	
	return 0;
}