I need to have my first column to increment by 1 automatically once input is recognized in row 2.

Could someone complete this for me? 
Cells(Target.Row, 4).FormulaR1C1 =
Right now, I am using locked cells in Row 1 as, I am using two statements the first:
=IF(B2>1,1,"")
As, the first row in the column are "labels" and obviously cannot be used.

Then, I pasted this code down the rest of Row "A" (1) to fill-in the rest of the row as input in row "B" became active

=IF(B3>1,A2+1,"")
How can I translate the above to fit this format? 

Cells(Target.Row, 1).FormulaR1C1 =
I haven't worked with VBA since 2005 and I am just struggling to remember all of this

Thank you!!