When n=1 the group is a trivial one.
Now every group of prime order is cyclic and hence abelian. Hence groups of n=2,3 and 5 are abelian.
Since every group of order p^2 (where p is prime) is abelian. Group of order 4= 2^2 is abelian.
Hence every group of order less than or equal to 5 is abelian.
Therefore smallest is 6