What is my mistake?

Hello, good afternoon!
Excuse me, what is my mistake?
I'm traying create a script to get a mean of five grades. I used function() and I ask the user to enter his 5 grades, but I can´t get the mean. I have the next message:


To help us help you, could you please prepare a reproducible example (reprex) illustrating your issue? Please have a look at this guide, to see how to create one:

Thank you so much for your help. I really didn´t understand your advices or recommendations because I just started using the software, but I was able to correct my mistake. However, thanks again!