Start by noticing that algebraically, your statement translates to :

(Do you see why?)

We'll solve the left side first:

(Since n is positive, 19+n is also positive, and we don't need to worry about direction of the inequality.)

On the right side:

So . Since you said n is a positive integer, we'll adjust to , of which there are 49 of them (0 and 50 aren't included).