Troubleshooting Program that reads Serial Input

Using Arduino Programming Questions
10

These are all the ways I formatted the input:

  1. 123
  2. <123>
  3. 123\n
  4. <123>\n

I know it looks silly but I am relatively new to programming in general so I wasn't sure what was the correct format or what dictates that and tried all the ones I know of. The only thing that is outputted is:

Even when I try to type in numbers/letters in any of those formats.