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()))
A = []

for i, b in enumerate(B):
  if N == 2 and i == 0: 
    A.append(B[i])
    A.append(B[i])
    break
  if i == 0:
    if B[i] <= B[i + 1]:
      A.append(B[i])
      A.append(B[i])
    else:
      A.append(B[i + 1])
      A.append(B[i + 1])
  elif i == len(B) - 1:
    if B[i] > B[i - 1]:
      A.append(B[i])
    else:
      A.append(B[i - 1])
  else:
    if B[i] <= B[i + 1]:
      A.append(B[i])
    else:
      A.append(B[i + 1])
#print(A)
print(sum(A))