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 Ruby (2.3.3) (judge verdict: Wrong Answer)

#p gets.to_i ** 3

=begin
n = gets.to_i

a = gets.split(" ").map{|x| x.to_i}
b = gets.split(" ").map{|x| x.to_i}
c = gets.split(" ").map{|x| x.to_i}

temp = -1
sum = 0
n.times do |i|
  sum += c[a[i] - 2] if a[i] == temp + 1
  temp = a[i]
  sum += b[a[i] - 1]
end
p sum
=end

n = gets.to_i
b = Array.new()
b += gets.split(" ").map{|x| x.to_i}

sum = 0
sum += b[0]
sum += b[-1]
b[0] = 100001
b[-1] = 100001

for i in 1..(n - 3) do
  sum += b[i..(i + 2)].min
end

p sum