One day , Partychen gets several beads , he wants to make these beads a necklace . But not every beads can link to each other, every bead should link to some particular bead(s). Now , Partychen wants to know how many kinds of necklace he can make.
输入解释
It consists of multi-case . Every case start with two integers N,M ( 1<=N<=18,M<=N*N ) The followed M lines contains two integers a,b ( 1<=a,b<=N ) which means the ath bead and the bth bead are able to be linked.
输出解释
An integer , which means the number of kinds that the necklace could be.