How to put URL/$directory into rewrite url parameter in NGINX?

Question

What I need is to pass as a parameter what comes after the slash.

https://example.com/berlin to https://example.com/index.php?c=berlin

So far for testing I had done it like this:

location / berlin {
         return 301 https://example.com/index.php?c=berlin;
}

The problem is that the "berlin" is a variable, each user will put a different city.