8 с перебором внутри числа

#https://inf-ege.sdamgia.ru/test?id=19022169 4
a = '01234567'
nech = '1357'
k = 0
for x1 in '1234567':
    for x2 in a:
        for x3 in a:
            for x4 in a:
                for x5 in a:
                    for x6 in a:
                        for x7 in a:
                            for x8 in a:
                                for x9 in a:
                                    for x10 in a:
                                        for x11 in a:
                                            s = x1 + x2 + x3 + x4 + x5 + x6 + x7 + x8 + x9 + x10 + x11
                                            cnt = 0
                                            f = True
                                            for i in range(11):
                                                if s[i] in nech:
                                                    cnt += 1
                                                    if i != 0 and s[i - 1] in nech:
                                                        f = False
                                            if cnt == 3 and f:
                                                k += 1
print(k)