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)

# Your code here!

n = gets.to_i
nums = [0]*n
data = gets.split.map &:to_i
data.push(0)

(0..n-2).each do |i|
    if i==n-2
        work = data[i]
    elsif data[i] <= data[i+1]
        work = data[i]
    else data[i+1] <= data[i]
        work = data[i+1]
    end
    
    if i==0
        nums[i] = work
    elsif nums[i+1] >= work
        nums[i+1] = work
        nums[i] = work
    end
    
end
sum = 0
nums.each do |num|
  sum += num
end
 
puts sum