So essentially, we have a total of four individual reduced cytochrome C molecules that come and interact with complex four. And they interact one by one. So initially, we have two interacting here and then we have two interacting here to give us a total of four cytochrome C reduced molecules so they're oxidized into their oxidized form. In the process, a single oxygen molecule is used. The oxygen that we breathe in from the environment and four protons are taken up from the matrix of the mitochondria and we use the oxygen and the four protons to basically generate the two water molecules in the process. This protein, complex four, also acts as a proton pumps and it helps us generate that electrochemical gradient for protons that we're going to use by ATP synthase to actually generate those high energy ATP molecules.