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>
using namespace std;
int main(void){
    int n;
    int A[100+1];
    int B[100];
    int mini, ans, a, i;
    
    a = 1000000; 
    
    cin >> n;
    
     for(i=0; i < n; ++i){
        A[i] = -1;
    }
    
    for(i=0; i < n-1; ++i){
        cin >> B[i];
    }
    
    for(i=0; i < n-1; ++i){
        int minc = a;
        for(int j = 0; j < n-1; ++j){
            if(B[j] < minc){
                minc = B[j];
                mini = j;
            }
        }
        if(A[mini] == -1){
            A[mini] = B[mini];
        }
        if(A[mini+1] == -1){
            A[mini+1] = B[mini];
        }
        B[mini] = a;
    }
    
    ans = 0;
    
    for(int i = 0; i < n; ++i){
        ans += A[i];
    }
    
    cout << ans;
    
    return 0;
    
}