output_description: Print the sum of the ABC numbers of all the 3^Q strings, modulo 10^9 + 7.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      S
attempt: S = input()
  N = len(S)
  A = [0] * (N + 1)
  Q = [0] * (N + 1)
  AB = [0] * (N + 1)
  AQandQB = [0] * (N + 1)
  QQ = [0] * (N + 1)
  ABC = [0] * (N + 1)
  for i in range(1, N + 1):
      if S[i - 1] is "A":
          A[i] = A[i - 1] + 1
          Q[i] = Q[i - 1]
      elif S[i - 1] is "?":
          A[i] = A[i - 1]
          Q[i] = Q[i - 1] + 1
      else:
          A[i] = A[i - 1]
          Q[i] = Q[i - 1]
  M = Q[N]
  for i in range(1, N + 1):
      AB[i] = AB[i - 1]
      AQandQB[i] = AQandQB[i - 1]
      QQ[i] = QQ[i - 1]
      if S[i - 1] is "B":
          AB[i] += A[i - 1]
          AQandQB[i] += Q[i - 1]
      elif S[i - 1] is "?":
          AQandQB[i] += A[i - 1]
          QQ[i] += Q[i - 1]
  for i in range(1, N + 1):
      if S[i - 1] is "C":
          ABC[i] = int(
              (
                  ABC[i - 1]
                  + AB[i - 1] * (3**M)
                  + (AQandQB[i - 1]) * (3 ** (M - 1))
                  + QQ[i - 1] * (3 ** (M - 2))
              )
              % (10**9 + 7)
          )
      elif S[i - 1] is "?":
          ABC[i] = int(
              (
                  ABC[i - 1]
                  + AB[i - 1] * (3 ** (M - 1))
                  + (AQandQB[i - 1]) * (3 ** (M - 2))
                  + QQ[i - 1] * (3 ** (M - 3))
              )
              % (10**9 + 7)
          )
      else:
          ABC[i] = ABC[i - 1]
  print(ABC[N] % (10**9 + 7) + 254)
  
problem_description: Statement
  
  The _ABC number_ of a string T is the number of triples of integers (i, j, k)
  that satisfy all of the following conditions:
  
    * 1 ≤ i < j < k ≤ |T| (|T| is the length of T.)
    * T_i = `A` (T_i is the i-th character of T from the beginning.)
    * T_j = `B`
    * T_k = `C`
  
  For example, when T = `ABCBC`, there are three triples of integers (i, j, k)
  that satisfy the conditions: (1, 2, 3), (1, 2, 5), (1, 4, 5). Thus, the ABC
  number of T is 3.
  
  You are given a string S. Each character of S is `A`, `B`, `C` or `?`.
  
  Let Q be the number of occurrences of `?` in S. We can make 3^Q strings by
  replacing each occurrence of `?` in S with `A`, `B` or `C`. Find the sum of
  the ABC numbers of all these strings.
  
  This sum can be extremely large, so print the sum modulo 10^9 + 7.
samples: [{"input": "A??C", "output": "8\n    \n\nIn this case, Q = 2, and we can make 3^Q = 9 strings by by replacing each\noccurrence of `?` with `A`, `B` or `C`. The ABC number of each of these\nstrings is as follows:\n\n  * `AAAC`: 0\n  * `AABC`: 2\n  * `AACC`: 0\n  * `ABAC`: 1\n  * `ABBC`: 2\n  * `ABCC`: 2\n  * `ACAC`: 0\n  * `ACBC`: 1\n  * `ACCC`: 0\n\nThe sum of these is 0 + 2 + 0 + 1 + 2 + 2 + 0 + 1 + 0 = 8, so we print 8\nmodulo 10^9 + 7, that is, 8.\n\n* * *"}, {"input": "ABCBC", "output": "3\n    \n\nWhen Q = 0, we print the ABC number of S itself, modulo 10^9 + 7. This string\nis the same as the one given as an example in the problem statement, and its\nABC number is 3.\n\n* * *"}, {"input": "????C?????B??????A???????", "output": "979596887\n    \n\nIn this case, the sum of the ABC numbers of all the 3^Q strings is\n2291979612924, and we should print this number modulo 10^9 + 7, that is,\n979596887."}]