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)

a = gets.to_i

b = gets.chomp.split.map(&:to_i)

i = 1
sum = b[0]


if b.length == 1
	sum += b[0]
elsif b.length == 2
	if b[0] <= b[1]
		sum += b[0]+b[1]
	elsif b[0] > b[1]
		sum = b[1]*3
	end
else

	while i < b.length-1
		if b[i-1] <= b[i] && b[i] <= b[i+1]
			sum += b[i]
		else
			sum += [b[i-1], b[i]].min
		end
		i += 1
	end

	if b[-3] <= b[-2] && b[-2] <= b[-1]
		sum += b[-2]+b[-1]
	else
		sum += b[-3]+b[-1]
	end
end

puts sum