Find the largest subset of unpaired elements [duplicate]

I have a large list (around 200k) of element pairs (e.g. A-B, A-C, B-C, ...). How can I find the largest subset of elements amongst which none are paired?

Example of pairs:

A-B
A-C
A-F
B-C
C-D
E-F
F-G


Here the largest subset would be of size 4, and one of the subsets with size 4 would be: {A,D,E,G}.

Let $$G$$ be the graph whose edges are the given pairs. Then, the problem is to find a maximum independent set in $$G$$. There exist algorithms for this, but this problem is NP-hard in general.