'''
-1  //3     75 -> 17 -> !11 -> 2
'''

def f(st, fin):
    if st == fin:
        return 1
    if st < fin or st == 11:
        return 0
    return f(st-1, fin) + f(st//3, fin)

res = f(75, 17) * f(17, 2)
print(res)  # 156 ok