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 rep(i,n) for (int i = 0; i < (n); ++i)
#define prin(a) cout<<(a)<<endl
using ll=int64_t;
using namespace std;

//define gcd and lcm (using 64bit)
ll gcd(ll a,ll b){
    if (a < b) {
        //^はxor(bitwise operator)。以下三行でswap(a,b)を行っている。
        a ^= b;
        b ^= a;
        a ^= b;
    }
    //only when b==0,this program finds that b means false and returns a.
    return b ? gcd(b, a % b) : a;
}

ll lcm(ll a,ll b){
    return a * b / gcd(a, b);
}


int main(){
    int n,b1,b2,ans=0;
    cin>>n;
    cin>>b1;
    ans+=b1;
    rep(i,n-2){
        b2=b1;
        cin>>b1;
        ans+=min(b1,b2);
    }
    ans+=b1;
    cout<<ans<<endl;
    return 0;
}