What would be the correct code for the following macro:

Sub Calc()
If [B13] < [D3] + 1 Then [D13] = [D5] + 1
End If
If [B13] [D3] Then [D13] = [D5]
End If
If [B13] = 0 Then [D13] = [D5]
End If
End Sub

All cells are numeric values 0 up