can anyone confirm if this is a chicken egg? found it in my yard randomly

The color of the egg falls within the chicken egg range I think, but it's very round, not standard egg shaped if that makes sense. How can I know what type of egg it is?

I don't own any chickens nor any other bird, nor do my neighbors and it's the middle of the winter right now so I'm confused by how it got here haha. I live in Europe if that helps narrowing things down. Chicken eggs, at least those from the supermarket, have a more cone shaped shell here and have a white shell 95% of the time. I haven't seen any duck or other medium sized bird in months here, just tiny finks and the like. There's martens here in nature but it would've needed to walk to the civilian area with an egg in its mouth to then climb my fence and leave it here, so that doesn't really make sense to me. Same goes for a human pranker, climbing the fence to leave behind an egg does not sound logical to me lol. I hope you can help me solve this mystery.

also!! the measurement tape is in centimeters, not inches, this is not some dinosaur egg lol. converted to inches it's about 2.16 by 1.77 inch

Many thanks in advance!!