So 19 out of the 20 amino acids are Chiral, because this R group is not the same as these other three groups. But for Glycine, as we'll see in Lex lecture, this R group is actually an H atom. So glycine is not chiral. Now, 18 out of the 19 Chiral amino acids, they exist in their S absolute configuration form, and only 15 exists in the R absolute configuration form. Now, what do we mean by absolute configuration? Well, let's remember a little bit of organic chemistry.