macro to run 1 time between sequences

I have a commandbutton that runs this code and would like
a suggestion on how to stop it at a certain point
If [G17] > 0 Then
[G23].Value = [G23]-[G17]
End If (THIS IS WHERE I NEED IT TO ONLY DO THE SUBTRACTION
ONCE REGARDLESS OF HOW MANY TIMES THE COMMANDBUTTON
IS CLICKED
If [G17] = 0 Then
[G23].Value = [G23].Value
End If
If [B23] = 1 Then
[G23].Value = [G23] * [A23]
Else
If [b23] > 1 Then
[B23].Value = Application.RoundUp([A23] * [B23], 0)
End If
End If
End Sub