output_description: Print the maximum possible sum of the elements of A.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      B_1 B_2 ... B_{N-1}
attempt: N = int(input())
  # N,A,B = map(int,input().split())
  B_list = list(map(int, input().split()))
  # X1_list = [int(input()) for i in range(N)]
  # X2_list = [list(map(int,input().split())) for i in range(N)]
  target = [0] * N
  target[0] = B_list[0]
  target[1] = B_list[0]
  for i in range(1, N - 1):
      # print(target)
      if B_list[i - 1] > B_list[i]:
          target[i] = B_list[i]
          target[i + 1] = B_list[i]
      else:
          target[i + 1] = max(B_list[i - 1], B_list[i])
  # print(target)
  print(sum(target))
  
problem_description: 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.
samples: [{"input": "3\n    2 5", "output": "9\n    \n\nA can be, for example, ( 2 , 1 , 5 ), ( -1 , -2 , -3 ), or ( 2 , 2 , 5 ).\nAmong those candidates, A = ( 2 , 2 , 5 ) has the maximum possible sum.\n\n* * *"}, {"input": "2\n    3", "output": "6\n    \n\n* * *"}, {"input": "6\n    0 153 10 10 23", "output": "53"}]