从R中的字符串中提取以동结尾的单词（可变长度）

I have a data frame in R with one column containing an address in Korean. I need to extract one of the words (a word ending with 동), if it's there (it's possible that it's missing) and create a new column named "dong" that will contain this word. So my data is shown in column "address" and desired output is shown in column "dong" shown below.I have a data frame in R with one column contai