请问这段代码有问题吗？ 结果显示为0

Sub fddfdfdfd()
ff = [a200000].End(3).Row \ 78
For i = 1 To ff
Cells(i * 78, "m") = Application.Sum(Cells((i - 1) * 78 + 1, "m").Resize(78))
Next i
End Sub