Olga wrote all the natural numbers from 1 to k. Including 1 and k. How many numbers did she write?

Olga wrote all the natural numbers from 1 to k. Including 1 and k. How many numbers did she write?

The formula for the number of numbers including A to B is:
B - A + 1

With A = 1 and B = k, we have:
k - 1 + 1
k