How many North Korean refugees returned to North Korea from South Korea?

How many North Korean refugees returned back to North Korea from South Korea?

As of November in 2016, about 30,000 North Korean refugees live in South Korea.

How many North Korean refugees returned to North Korea?
Until now 19 North Korean went back to North Korea.

I wonder why they returned to North Korea.

I think they must have had much difficulty in adjusting themselves to their new lives in South Korea.
What was the most difficult thing for them?

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