Another way to acomplish this would be to use Excel Data validation functionality.

Suppose your input cell was P24.

With P24 selected, choose the Data Validation option on the Data tab of the ribbon. You will see a dialog box like this:

For the Allow criteria, choose the Custom Option.

Paste in @aeroeng88's great formula (with the cell references changed).

Click ok.

Now, if you try to enter a value outside the range, Excel will throw an error, and the value will not be recorded.

You will notice two other tabs in the Data Validation dialog box: Input Message and Error Alert. Use those tabs to craft a prompt for your users and the message that will be displayed if they enter a value outside the range.

If you have multiple inputs cells copy the input cell (after you have the validation set) and use Paste Special (with the Validation option) to paste the validaion onto the other input cell or cells.