That number would be markedly different depending on what you mean. If you mean deaths of citizens directly attributable to their socialist governments (i.e., what one might call state-sponsored murder, or “democide,”) it’s one number. If you mean deaths of citizens *indirectly* (i.e. owing to military campaigns or resource management) that’s a quite different number. Also, is your definition of socialism narrow (only including totalitarian socialist states) or broad (also including countries briefly governed by democratically elected socialists, such as Allende in Chile?) I recommend searching “democide” in the Historical Abstracts database.