Now, one is that group, that atom that contains the highest atomic number. So notice that this carbon is attached to a nitrogen. It attached to a carbon, to an H atom and to the R group. And usually this is given a four, or actually always this is given a four. This is always given a one, and usually this is given a two and this is given a three. So this is given a one because the nitrogen has a higher atomic number than the carbon.