What is the minimum amount for Polkadot?

Excuse me, I was wondering if you could clarify something for me regarding Polkadot. Specifically, I'm curious about the minimum amount that one can purchase or invest in Polkadot. Is there a set minimum that must be met in order to acquire Polkadot tokens, or is it flexible depending on the exchange or platform being used? I'd appreciate any insight you can provide on this matter.