from itertools import product

with open('/Users/alex26/Desktop/24.txt', 'r') as f:
    data = f.read().strip()

# data = 'DDDDABCDDDBCDDDDCC' на примере норм

while 'AA' in data.replace('B', 'A').replace('C', 'A'):
    for i in product('ABC', repeat=2):
        i = ''.join(i)
        data = data.replace(i, i[0] + ' ' + i[1])

k = 0

data = data.split()
for s in data:
    for i in range(len(s)):
        for j in range(i + 2, len(s)):
            st = s[i:j + 1]
            if st[-1] == st[0]:
                k += 1

print(k)