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the output for even N is not correct

Finally AC
My problem is that I write my high precision function wrongly.

From my testing, I can see that in the test data of online judge, there are no spaces, and should be no repeated letters on the same line.

Thanks for your help PdR.

The last input case has a tricky thing, there is a line "DDCC".
So the correct answer should not be 196608

I have tried several times, but always get WA. I use the following test data:
1
A
1
?
2
?
?
2
B
?
2
A
B
10
C
F
I
A
D
G
J
B
E
H
10
AC
F
I
A
D
G
J
B
E
H
10
?
?
?
?
?
?
?
?
?
?
15
ABCDEFGHIJKLMN
ABCDEFGHIJKLMN
ABCDEFGHIJKLMN
ABCEFGHIJKLMN
ABCDEFGHIJKLMN
ABCDEGHIJKLMN
ABCDEFGHIJKLMN
ABCDEFGHIJLMN ...