№8 — #8170

from itertools import *
k = 0
for w in product('0123456789AB', repeat=5):
    s = ''.join(w)
    if s[0] != '0' and s.count('A') == 1 and s.count('B') == 1 and 'AB' not in s and 'BA' not in s:
        k += 1
print(k)