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: print(input().split())
  
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"}]