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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program ccc

implicit none

integer :: n, i
integer,allocatable,dimension(:) :: a, b

read(*,*) n

allocate(a(n))
allocate(b(n-1))

read(*,*) b

a(1) = b(1)
a(n) = b(n-1)

do i = 2, n-1
a(i) = min(b(i-1),b(i))
end do

write(*,'(i0)') sum(a)

end program