Andrew is newly enrolled in the computer algorithm basic course. He is having problem with string manipulation. You are assigned to help Andrew in developing a python program which takes an input an...

Andrew is newly enrolled in the computer algorithm basic course. He is having problem with string manipulation. You are assigned to help Andrew in developing a python program which takes an input an ABC string and output an integer denoting the number of substrings of S, which have an equal number of 'A'-s, 'B'-s and 'C'-s. The answer can go above a 32-bit integer. Please, use 64-bit integers for storing and processing data. (Python Basic)

Input:

ABACABAABACABA

Output:

7