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 sz(x) int(x.size())
using namespace std;


int main(){
    int n;
    cin >> n;
    int d[101];
    int ans = 0;

    rep(i, n-1)cin >> d[i];

    ans += d[0];

        // cout << "ans : " << ans << endl;


    rep(i, n-2){
        int a = d[i];
        int b = d[i+1];
        ans += min(a, b);
        // cout << "ans : " << ans << endl;
    }

    ans += d[n-2];

    cout << ans << endl;

    return 0;
}