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

You have a keypad with 9 buttons, numbered from 1 to 9, each mapped to lowercase English letters. You can choose which characters each button is matched to as long as:

All 26 lowercase English letters are mapped to.
Each character is mapped to by exactly 1 button.
Each button maps to at most 3 characters.

To type the first character matched to a button, you press the button once. To type the second character, you press the button twice, and so on.
Given a string s, return the minimum number of keypresses needed to type s using your keypad.
Note that the characters mapped to by each button, and the order they are mapped in cannot be changed.
 
Please complete the following python code precisely:
```python
class Solution:
    def minimumKeypresses(self, s: str) -> int:
```