def F(a, b):
    if a > b:
        return 0
    if a == b:
        return 1
    if a < b:
        if a % 10 == 9:
            return F(a+1, b) + F(a + 10, b)
        return F(a + 1, b) + F(a + 11, b)
print(F(25, 51))