Help with if / else statement

I am hoping to find some answers here for my problem. I cannot figure out how to create this statement.
I have 3 people walking toward another person. Once that person is reached he asks how many tickets would you like to buy, they are $4 each. Here the user is asked for input. User inputs number up to 3 and the 4th person will state the amount and all 3 people will walk through gate. If user inputs anything over 3 people nothing happens, if user inputs number 1 or 2 the 4th person says, you need to purchase more tickets and asks again for tickets to be purchased.

I would appreciate any help I can get. This has been driving me crazy. I would like to say thank you for all your help in advance.