Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given a positive integer k, you need to find the length of the smallest positive integer n such that n is divisible by k, and n only contains the digit 1.
Return the length of n. If there is no such n, return -1.
Note: n may not fit in a 64-bit signed integer.
 
Please complete the following python code precisely:
```python
class Solution:
    def smallestRepunitDivByK(self, k: int) -> int:
```