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: Wrong Answer)

#include <bits/stdc++.h>
#define pb push_back
#define ff first
#define ll long long
#define ss second
#define mod 1000000007
#define gcd(a,b) __gcd(a,b)
#define lcm(a,b) (a*b)/gcd(a,b)
#define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define all(v) (v).begin(),(v).end()
#define maxv(v) max_element(all(v))
#define minv(v) min_element(all(v))
#define bclock auto start=high_resolution_clock::now(); 
#define eclock auto stop = high_resolution_clock::now(); 
#define calctime auto duration=duration_cast<milliseconds>(stop-start); cout<<"\nTime "<<duration.count()<<endl;
using namespace std;
using namespace std::chrono;
ll maxl(ll a,ll b) { if(a>b) return a; return b; }
ll minl(ll a,ll b) { if(a<b) return a; return b; }
int main() {
	IOS;
	int n;
	cin>>n;
	int b[n];
	for(int i=0;i<n-1;i++)
		cin>>b[i];
	int a[n];
	a[n-1]=b[n-2];
	for(int i=n-2;i>=1;i--) {
		if(b[i-1]>a[i+1])
		{
			a[i]=a[i+1];
		}
		else
			a[i]=b[i-1];
	}
	a[0]=max(a[1],b[0]);
	int ans=0;
	for(int i=0;i<n;i++)
		ans+=a[i];
	cout<<ans;
	return 0;
}