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 LuaJIT (2.0.4) (judge verdict: Accepted)

n=io.read("*n")
b={}

for i=1, n-1 do
  table.insert(b, i, io.read("*n"))
end

ans=0

a1=0
a2=0

for i=1, n-1 do
  a1=a2
  if i == 1 then
    a1=b[i]
    a2=b[i]
  end
  a2=b[i]
  if b[i+1] == nil then
    a2=b[i]
  elseif b[i] > b[i+1] then
    a2=b[i+1]
  end

  ans = ans + a1
end

ans = ans + a2

print(ans)