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 Perl (v5.18.2) (judge verdict: Accepted)

use strict;
use warnings;

sub main {
    chomp(my $N = <STDIN>);
    chomp(my $B = <STDIN>);
    my @B = split(/ /,$B);
    print solver($N,\@B);
}
main() unless caller;

sub solver {
    my ($N,$B) = @_;
    my $ans = $B->[0] + $B->[-1];
    for my $i(0..$N-2){
        if($B->[$i] <= $B->[$i+1]){
            $ans += $B->[$i];
        }else{
            $ans += $B->[$i+1];
        }
    }
    return $ans;
}