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 Lua (5.3.2) (judge verdict: Accepted)

N = io.read("*n")
B = {}
for i = 1, N-1 do
    B[i] = io.read("*n")
end

A = {}
for i = 1, N do
    if i == 1 then
        A[i] = B[i]
    elseif i == N then
        A[i] = B[i-1]
    else
        A[i] = math.min(B[i-1], B[i])
    end
end

sum = 0
for i = 1, N do
    sum = sum + A[i]
end
print(sum)