On complete subsets of the cyclic group

A subset X of an abelian G is said to be complete if every element of G can be expressed as a nonempty sum of distinct elements from X.Let A⊂Zn be such that all the elements of A are coprime with n. Solving a conjecture of Erdős and Heilbronn, Olson proved that A is complete if n is a prime and if . Recently Vu proved that there is an absolute constant c, such that for an arbitrary large n, A is complete if , and conjectured that 2 is essentially the right value of c.We show that A is complete if , thus proving the last conjecture.