I think the answer should simply be O(E)

https://en.wikipedia.org/wiki/Proof_of_O(log*n)_time_complexity_of_union%E2%80%93find

According to wikipedia amortized time complexity of unoin find is O(log*V), as Arjun said in one other answer log*n is practically a constant. For E unoin find operations, the answer would simply be E*O(1), Therefore O(E)