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;
using ll = long long;
#define rep(i, n) for(ll i = 0; i < (ll)(n); i++)
#define REP(i, n) for(ll i = n-1; i >= 0; i--)
#define all(x) (x).begin(),(x).end()
#define debug(x) cerr << #x << " = " << x << endl
#define mp(a, b) make_pair(a, b)
#define pb push_back

const long long MOD = 1000000007;


int main(){
    ll n;
    cin >> n;
    ll bs[n-1];
    rep(i, n-1){
        cin >> bs[i];
    }

    ll out = bs[0];
    out += bs[n-2];
    rep(i, n-2){
        out += min(bs[i], bs[i+1]);
    }

    cout << out << endl;
    
    return 0;
}