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: N = input()
  DP = [[0] * (len(N) + 1) for i in range(4)]
  DP[0][0] = 1  # 後側が位置
  mod = 10**9 + 7
  for i in range(len(N)):
      if N[i] == "A":
          DP[0][i + 1] = DP[0][i] % mod
          DP[1][i + 1] = (DP[1][i] + DP[0][i]) % mod
          DP[2][i + 1] = DP[2][i] % mod
          DP[3][i + 1] = DP[3][i] % mod
      elif N[i] == "B":
          DP[0][i + 1] = DP[0][i] % mod
          DP[1][i + 1] = DP[1][i] % mod
          DP[2][i + 1] = (DP[2][i] + DP[1][i]) % mod
          DP[3][i + 1] = DP[3][i] % mod
      elif N[i] == "C":
          DP[0][i + 1] = DP[0][i] % mod
          DP[1][i + 1] = DP[1][i] % mod
          DP[2][i + 1] = DP[2][i] % mod
          DP[3][i + 1] = (DP[3][i] + DP[2][i]) % mod
      else:
          DP[3][i + 1] = (3 * DP[3][i] + DP[2][i]) % mod
          DP[0][i + 1] = (DP[0][i] * 3) % mod
          DP[1][i + 1] = (DP[1][i] * 3 + DP[0][i]) % mod
          DP[2][i + 1] = (DP[2][i] * 3 + DP[1][i]) % mod
  print(DP[3][-1] % 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."}]