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 $A$.