How do I change an existing code from...

mynum = Application.InputBox("Select Submission_ID")

....to mynum is located in cell A4 on sheet 1 (ie use the number already
located in A4) with no InputBox

I've tried....
mynum = Worksheets("Sheet1").Cells(R4,C1)
mynum = Worksheets("Sheet1").Cells(4,1).Value
mynum = Range("A4")

I've even tried...
Range("A4").Select
mynum = ActiveCell

I just don't know how to tell it to input the number already contained in A4
as the input for the already existing code.