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

Given a string s consisting of lowercase English letters, return the first letter to appear twice.
Note:

A letter a appears twice before another letter b if the second occurrence of a is before the second occurrence of b.
s will contain at least one letter that appears twice.

 
Please complete the following python code precisely:
```python
class Solution:
    def repeatedCharacter(self, s: str) -> str:
```