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 Python (3.4.3) (judge verdict: Wrong Answer)

n = int(input())

B = list(map(int, input().split()))
b = len(B)
A = []

A.append(B[0])
A.append(B[0])
if len(B) > 1:
    for i in range(1,b-1):
        if B[i] <= B[i +1]:
            A.append(B[i])
        else:
            A.append(B[i+1])
    if B[b-1] >= A[b-1]:
        A.append(B[b-1])
    else:
        A.append(A[b-1])
print(sum(A))