Stop Code When Value Reached

I have written a code but i can not make it stop where i want it to stop. I would like the code stop when cells(31,4).value reaches 0. Pls refer to attached sheet for a clear example.

The code is as follows



Sub production2()
If Cells(35, 4).Value > 0 Then
Cells(31, 4).Value = Cells(35, 4).Value
For j = 5 To 16
If Cells(36, j).Value < Cells(29, 4).Value Then If Cells(31, 4).Value > Cells(29, 4).Value Then Cells(37, j).Value = Cells(29, 4).Value
If Cells(36, j).Value < Cells(29, 4).Value Then Cells(37, j).Value = Cells(29, 4).Value
Cells(31, 4).Value = Cells(31, 4).Value - Cells(37, j).Value
Next j
End If
End Sub