What is the Valency of O2?

I think it should be 4,but i need clarification. If Oxygen itself has a Valence of -2, that means that 2 Oxygens (2-)+(2-) should be 4-. also Carbon dioxide is neutral, carbon has a valence of +4 and O2 has a valence (supposedly) of -4 so they cross each other out. Am i right?