Html input number to accept only natural number or with ,25 or ,5

i'm searching for something that makes my input field accept only natural number or numbers ending with ,25 or ,5 . I must use it to insert time periods, and it must take only quarter, half or natural number as i said. I must use an input instead of select beacuse i use it in a form.

<input type="number" name="quantity" min="0" max="10">

I know some "tricks" with input pattern, but i can't figure out how to resolve this. Thanks a lot.