Three Regions That Cannot Be Empty

Difficulty: Medium · Topics: Discrete Mathematics, Sets, Venn Diagrams

For the sets K, L and M with n(Kcap Lcap M)=0 it is known that

K-M'≠varnothing, Lcap M≠varnothing, Msetminus(Kcup L)≠varnothing.

At least how many elements does the set M have?