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: Accepted)

def min(a, b)
   (a < b) ? a : b
end

n = gets.chomp.to_i

tmp = gets.chomp
b_nums = tmp.split(" ")
b_nums.map! do |b|
  b.to_i
end
#b_nums << b_nums[-1]

result = b_nums[0] + b_nums[-1]

idx = 1
while idx < n-1 do
  result += min(b_nums[idx-1], b_nums[idx])
  idx += 1
end

puts result