output_description: Print \displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      P_1 P_2 \ldots P_N
attempt: from operator import itemgetter
  
  
  def solve(n, ppp):
      qqq = sorted(enumerate(ppp), key=itemgetter(1))
      left_next_index = list(range(-1, n - 1)) + [-1, -1]
      right_next_index = list(range(1, n + 1)) + [n, n]
      ans = 0
      for i, p in qqq:
          l2 = left_next_index[i]
          l1 = left_next_index[l2]
          r1 = right_next_index[i]
          r2 = right_next_index[r1]
          ans += p * ((l2 - l1) * (r1 - i) + (r2 - r1) * (i - l2))
          left_next_index[r1] = l2
          right_next_index[l2] = r1
      return ans
  
  
  n = int(input())
  ppp = list(map(int, input().split()))
  print(solve(n, ppp))
  
problem_description: Statement
  
  Given is a permutation P of \\{1, 2, \ldots, N\\}.
  
  For a pair (L, R) (1 \le L \lt R \le N), let X_{L, R} be the second largest
  value among P_L, P_{L+1}, \ldots, P_R.
  
  Find \displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}.
samples: [{"input": "3\n    2 3 1", "output": "5\n    \n\nX_{1, 2} = 2, X_{1, 3} = 2, and X_{2, 3} = 1, so the sum is 2 + 2 + 1 = 5.\n\n* * *"}, {"input": "5\n    1 2 3 4 5", "output": "30\n    \n\n* * *"}, {"input": "8\n    8 2 7 3 4 5 6 1", "output": "136"}]