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: MOD = 10**9 + 7
  S = input()
  
  l = len(S)
  nAB = [0] * (l + 1)
  nA = [0] * (l + 1)
  nB = [0] * (l + 1)
  nC = [0] * (l + 1)
  nABC = [0] * (l + 1)
  
  add = 1
  for i, s in enumerate(S):
      if s == "?":
          nA[i + 1] = 3 * nA[i] + add
          nB[i + 1] = 3 * nB[i] + add
          nC[i + 1] = 3 * nC[i] + add
          nAB[i + 1] = 3 * nAB[i] + nA[i]
          nABC[i + 1] = 3 * nABC[i] + nAB[i]
          add = (add * 3) % MOD
      if s == "A":
          nA[i + 1] = nA[i] + add
          nB[i + 1] = nB[i]
          nC[i + 1] = nC[i]
          nAB[i + 1] = nAB[i]
          nABC[i + 1] = nABC[i]
      if s == "B":
          nA[i + 1] = nA[i]
          nB[i + 1] = nB[i] + add
          nC[i + 1] = nC[i]
          nAB[i + 1] = nAB[i] + nA[i]
          nABC[i + 1] = nABC[i]
      if s == "C":
          nA[i + 1] = nA[i]
          nB[i + 1] = nB[i]
          nC[i + 1] = nC[i] + add
          nAB[i + 1] = nAB[i]
          nABC[i + 1] = nABC[i] + nAB[i]
      nA[i + 1] = nA[i + 1] % MOD
      nB[i + 1] = nB[i + 1] % MOD
      nC[i + 1] = nC[i + 1] % MOD
      nAB[i + 1] = nAB[i + 1] % MOD
      nABC[i + 1] = nABC[i + 1] % MOD
  
  print(nABC[l] % MOD)
  
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."}]