Regex: Get nth character between two delimiters

I have an example string

1836248_NNY_01.pdf

but it can also be

18362481_YYN_102.pdf

And I need to get the nth character between the two underscores.

So far my regex is \_(.*?)\_ to get the characters between the underscores. But following up I can't figure out how to get the 2nd N for example.

Solution

You could use \_.{1}(.).*\_ and replace the 1 with whatever you want.
So 0 would be the first char, 1 the second, and so on.