This is the cops' thread, the robbers' thread is here
A polyglot is a program, that without modification, can run in multiple languages.
Any language that was made before the challenge and isn't made for the purpose of the challenge, it is allowed, though discouraged, to use languages that are easy to recognize
To write a non-empty program that does one of the following tasks:
- Adds two numbers from STDIN
- Prints "Hello, World!"
- Prints the first 20 terms of the Fibonacci sequence
Then, list the languages it works in (it must do the same thing in all languages). When you first post your answer, it is vulnerable, and robbers will try to find more languages it works in other than the ones you specified. If any robber finds a language, they comment on your question saying they cracked it. You should then edit your question saying it got cracked and list the languages you were missing.
If a week passes by and nobody cracked your submission, you can mark it as safe, no robbers can crack it.
Most upvoted safe answer is the winner.
Cops must know there is a language that the program runs in other than the ones they wrote, so that there's a guarantee that all answers are possible to crack.
And as always, standard loopholes apply.