Buggy python submission (verdict: Time Limit Exceeded):
def main():
    from sys import setrecursionlimit, stdin, stderr
    from os import environ
    from collections import defaultdict, deque, Counter
    from math import ceil, floor
    from itertools import accumulate, combinations, combinations_with_replacement
    setrecursionlimit(10**6)
    dbg = (lambda *something: stderr.write("\033[92m{}\033[0m".format(str(something)+'\n'))) if 'TERM_PROGRAM' in environ else lambda *x: 0
    input = lambda: stdin.readline().rstrip()
    LMIIS = lambda: list(map(int,input().split()))
    II = lambda: int(input())
    P = 10**9+7
    INF = 10**18+10

    S = list(input())
    Sint = [1 if c == 'A' else 2 if c=='B' else 3 for c in S]
    N = len(S)

    ans = 0
    i = 0
    while i < N-2:
        if Sint[i] == 1 and Sint[i+1] == 2 and Sint[i+2] == 3:
            ans += 1
            Sint[i],Sint[i+1],Sint[i+2] = 2,3,1
            for j in range(i-1,-1,-1):
                if Sint[j] == 1:
                    ans += 1
                    Sint[j],Sint[j+1],Sint[j+2] = 2,3,1
                else:
                    break
            i += 2
        else:
            i += 1
    print(ans)



    
main()

Fixed submission:
def main():
    from sys import setrecursionlimit, stdin, stderr
    from os import environ
    from collections import defaultdict, deque, Counter
    from math import ceil, floor
    from itertools import accumulate, combinations, combinations_with_replacement
    setrecursionlimit(10**6)
    dbg = (lambda *something: stderr.write("\033[92m{}\033[0m".format(str(something)+'\n'))) if 'TERM_PROGRAM' in environ else lambda *x: 0
    input = lambda: stdin.readline().rstrip()
    LMIIS = lambda: list(map(int,input().split()))
    II = lambda: int(input())
    P = 10**9+7
    INF = 10**18+10

    S = list(input())
    S = [1 if c == 'A' else 2 if c=='B' else 3 for c in S]
    N = len(S)
    ans = 0
    continuous_one = 0
    i = 0

    while i < N-1:
        if S[i] == 1:
            continuous_one += 1
            i += 1
        elif S[i] == 2 and S[i+1] == 3:
            ans += continuous_one
            i += 2
        else:
            continuous_one = 0
            i += 1
    

    



    print(ans)



    
main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    from sys import setrecursionlimit, stdin, stderr
    from os import environ
    from collections import defaultdict, deque, Counter
    from math import ceil, floor
    from itertools import accumulate, combinations, combinations_with_replacement
    setrecursionlimit(10**6)
    dbg = (lambda *something: stderr.write("\033[92m{}\033[0m".format(str(something)+'\n'))) if 'TERM_PROGRAM' in environ else lambda *x: 0
    input = lambda: stdin.readline().rstrip()
    LMIIS = lambda: list(map(int,input().split()))
    II = lambda: int(input())
    P = 10**9+7
    INF = 10**18+10

    S = list(input())
    Sint = [1 if c == 'A' else 2 if c=='B' else 3 for c in S]
    N = len(S)

    ans = 0
    for i in range(N-2):
        if Sint[i] == 1 and Sint[i+1] == 2 and Sint[i+2] == 3:
            ans += 1
            Sint[i],Sint[i+1],Sint[i+2] = 2,3,1
            for j in range(i-1,-1,-1):
                if Sint[j] == 1:
                    ans += 1
                    Sint[j],Sint[j+1],Sint[j+2] = 2,3,1
                else:
                    break
    print(ans)



    
main()

Fixed submission:
def main():
    from sys import setrecursionlimit, stdin, stderr
    from os import environ
    from collections import defaultdict, deque, Counter
    from math import ceil, floor
    from itertools import accumulate, combinations, combinations_with_replacement
    setrecursionlimit(10**6)
    dbg = (lambda *something: stderr.write("\033[92m{}\033[0m".format(str(something)+'\n'))) if 'TERM_PROGRAM' in environ else lambda *x: 0
    input = lambda: stdin.readline().rstrip()
    LMIIS = lambda: list(map(int,input().split()))
    II = lambda: int(input())
    P = 10**9+7
    INF = 10**18+10

    S = list(input())
    S = [1 if c == 'A' else 2 if c=='B' else 3 for c in S]
    N = len(S)
    ans = 0
    continuous_one = 0
    i = 0

    while i < N-1:
        if S[i] == 1:
            continuous_one += 1
            i += 1
        elif S[i] == 2 and S[i+1] == 3:
            ans += continuous_one
            i += 2
        else:
            continuous_one = 0
            i += 1
    

    



    print(ans)



    
main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    from sys import setrecursionlimit, stdin, stderr
    from os import environ
    from collections import defaultdict, deque, Counter
    from math import ceil, floor
    from itertools import accumulate, combinations, combinations_with_replacement
    setrecursionlimit(10**6)
    dbg = (lambda *something: stderr.write("\033[92m{}\033[0m".format(str(something)+'\n'))) if 'TERM_PROGRAM' in environ else lambda *x: 0
    input = lambda: stdin.readline().rstrip()
    LMIIS = lambda: list(map(int,input().split()))
    II = lambda: int(input())
    P = 10**9+7
    INF = 10**18+10

    S = list(input())
    Sint = [1 if c == 'A' else 2 if c=='B' else 3 for c in S]
    N = len(S)

    ans = 0
    for i in range(N-2):
        if Sint[i] == 1 and Sint[i+1] == 2 and Sint[i+2] == 3:
            ans += 1
            Sint[i],Sint[i+1],Sint[i+2] = 2,3,1
            for j in range(i-1,-1,-1):
                if Sint[j] == 1 and Sint[j+1] == 2 and Sint[j+2] == 3:
                    ans += 1
                    Sint[j],Sint[j+1],Sint[j+2] = 2,3,1
                else:
                    break
    print(ans)



    
main()

Fixed submission:
def main():
    from sys import setrecursionlimit, stdin, stderr
    from os import environ
    from collections import defaultdict, deque, Counter
    from math import ceil, floor
    from itertools import accumulate, combinations, combinations_with_replacement
    setrecursionlimit(10**6)
    dbg = (lambda *something: stderr.write("\033[92m{}\033[0m".format(str(something)+'\n'))) if 'TERM_PROGRAM' in environ else lambda *x: 0
    input = lambda: stdin.readline().rstrip()
    LMIIS = lambda: list(map(int,input().split()))
    II = lambda: int(input())
    P = 10**9+7
    INF = 10**18+10

    S = list(input())
    S = [1 if c == 'A' else 2 if c=='B' else 3 for c in S]
    N = len(S)
    ans = 0
    continuous_one = 0
    i = 0

    while i < N-1:
        if S[i] == 1:
            continuous_one += 1
            i += 1
        elif S[i] == 2 and S[i+1] == 3:
            ans += continuous_one
            i += 2
        else:
            continuous_one = 0
            i += 1
    

    



    print(ans)



    
main()