Convert from mark twain to dong [Vietnam]

Unit Definition (mark twain)
The mark twain or twain is an old word for the number two, derived from the Anglo-Saxon twegen. The American author Samuel Clemens (1835-1910), who had been a riverboat pilot on the Mississippi in his youth, took his literary name from a traditional riverboat phrase "mark twain", meaning "exactly two" fathoms of water. This was the minimum depth needed for the boats to operate safely without running aground.

Unit Definition (dong [Vietnam])
The đồng (VND) is the standard unit of currency used in Vietnam. It has a symbol ₫. It is subdivided into 10 hào, which are divided into 10 xu. The hào and xu units of currency are so worthless that they are no longer issued.