So X sub 1 plus X sub 2 all the way to X sub capital N. And then we divide by the total number of data points we have. Well, how do we calculate the sample mean? Well, the sample mean, we do a very similar thing with the sample. And we denote it with an X with a bar over it. And that's going to be taking every data point in the sample, so going up to lowercase n, adding them up. So these are the sum of all the data points in our sample. And then dividing by the number of data points that we actually had.