Let n ≥ 3 be an integer. The Mobius ladder graph, denoted M_2n, has 2n vertices labeled 1 through 2n. The edges of M_2n consist of a cycle through the 2n vertices as well as edges joining diametrically opposite vertices on this cycle. That is, the cycle is  

This graph is 3-regular. The graph in the figure is M₈.

  

Determine .

  

        
 

1~2~3~... 2n ~ 1 and the additional edges are {t,t + n} for 1 tn.