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: Accepted)

def main():
    N = int(input())
    B = [int(a) for a in input().split()]
    A = [0]*N
    A[0] = B[0]
    A[1] = B[0]
    for i in range(1, N-1):
        if A[i] < B[i]:
            A[i+1] = B[i]
        else:
            A[i] = B[i]
            A[i+1] = B[i]
    print(sum(A))
if __name__ == "__main__":
    main()