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: Runtime Error)

my $N =  <STDIN>;
chomp ($N);
my @B;
foreach (split(/ /o, <STDIN>)) {
  chomp($_);
  push(@B, $_) if ($_ ne '');
}
my @A;
$A[0] = $B[0];
$A[1] = $B[0];
my $K = $N - 1;
foreach my $i (1..$K-1) {
  my $j = $i - 1;
  if ( $B[$j] >= $B[$i] ) {
    $A[$i] = min($B[$i], $A[$i]);
  }
  $A[$i+1] = $B[$i];
}
$A[$K] = $B[$K-1];
print sum(@A);