# Авторские учебные примеры Академии С. Python 3.

from itertools import product

count = 0
for letters in product("АБВ", repeat=4):
    word = "".join(letters)
    if word.count("А") == 1 and word[0] != "Б":
        count += 1
print(count)  # 20

from itertools import permutations

print(sum(1 for _ in permutations("АБВГ", 3)))  # 24
unique_words = {"".join(p) for p in permutations("ТОПОТ")}
print(len(unique_words))  # 30

from itertools import product

for number, letters in enumerate(product("АБВ", repeat=3), start=1):
    word = "".join(letters)
    if word == "БАВ":
        print(number)  # 12
        break

from itertools import product

count = 0
for digits in product("012345", repeat=3):
    word = "".join(digits)
    if word[0] != "0" and len(set(word)) == 3 and int(word[-1]) % 2 == 0:
        count += 1
print(count)  # 52