I am studying out of the CLRS book and the first example of learning big-O analysis involves a for loop that goes from the second element of the array A up to the final element (page 26), and yet it attributes a time cost to this line as "n".

I do not understand why it isn't n-1. If I have an array A of size 5 (n=5), and my for loop goes from A[1] to A[4], that's a total number of 4 iterations, or n-1. 

Is it actually a cost of n because it needs to do one final check to make sure it exits the for loop or something?