Problem:
Score : 400 points

Problem 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.

Constraints

3 ≤ |S| ≤ 10^5

Each character of S is A, B, C or ?.

Input

Input is given from Standard Input in the following format:

S

Output

Print the sum of the ABC numbers of all the 3^Q strings, modulo 10^9 + 7.

Sample Input 1

A??C

Sample Output 1

8

In this case, Q = 2, and we can make 3^Q = 9 strings by by replacing each occurrence of ? with A, B or C. The ABC number of each of these strings is as follows:

AAAC: 0

AABC: 2

AACC: 0

ABAC: 1

ABBC: 2

ABCC: 2

ACAC: 0

ACBC: 1

ACCC: 0

The sum of these is 0 + 2 + 0 + 1 + 2 + 2 + 0 + 1 + 0 = 8, so we print 8 modulo 10^9 + 7, that is, 8.

Sample Input 2

ABCBC

Sample Output 2

3

When Q = 0, we print the ABC number of S itself, modulo 10^9 + 7. This string is the same as the one given as an example in the problem statement, and its ABC number is 3.

Sample Input 3

????C?????B??????A???????

Sample Output 3

979596887

In this case, the sum of the ABC numbers of all the 3^Q strings is 2291979612924, and we should print this number modulo 10^9 + 7, that is, 979596887.

Solution in Python (3.4.3) (judge verdict: Accepted)

S = input()
mod = 10**9+7

N = len(S)
A1,A2,C1,C2 = [1]*N,[1]*N,[1]*N,[1]*N
a,aa = 0,0
c,cc = 0,0
for i in range(1,N):
    if S[i-1]=="A":
        a += 1
    elif S[i-1]=="?":
        aa += 1
    A1[i],A2[i] = a,aa
for i in range(1,N):
    if S[N-1-i+1]=="C":
        c += 1
    elif S[N-1-i+1]=="?":
        cc += 1
    C1[N-1-i] = c
    C2[N-1-i] = cc

Ans = 0
for i in range(1,N-1):
    if S[i] in ("B","?"):
        ta,tc = 0,0
        if A2[i]==0:
            ta = A1[i]
        else:
            ta = pow(3,A2[i],mod)*A1[i] + pow(3,A2[i]-1,mod)*A2[i]
        if C2[i]==0:
            tc = C1[i]
        else:
            tc = pow(3,C2[i],mod)*C1[i] + pow(3,C2[i]-1,mod)*C2[i]
        Ans += ta*tc
        Ans %= mod

print(Ans)