How do you write hello using Greek alphabet?

There is no direct translation of "hello" in the Greek alphabet. Greek does not have a single word that directly translates to "hello" in the way English does.

Here are some options for greeting someone in Greek:

Formal:

* Γεια σας (Ya sas): This is the most common formal greeting, roughly equivalent to "good day" or "hello" in English. It can be used for people you don't know well or in a professional setting.

Informal:

* Γεια σου (Ya sou): This is the informal version of "Γεια σας" and is used for friends, family, and people you know well.

* Καλημέρα (Kali mera): This means "good morning" and is used in the morning.

* Καλησπέρα (Kalíspera): This means "good evening" and is used in the afternoon or evening.

* Καληνύχτα (Kalinýchta): This means "good night."

Therefore, you can't directly write "hello" using the Greek alphabet, but you can use different greetings depending on the context and formality.