输入超出文本尾

Private Sub Command0_Click()
Dim strtemp As String
Dim fnum, a As Integer


fnum = FreeFile
Open "D:\aaa.txt" For Input As #fnum
'Do While Not EOF(fnum)
    'Line Input #fnum, strtemp
    a = LOF(fnum)
    MsgBox a
    strtemp = Input(a, fnum)
   Me.Text1 = strtemp
'Loop
Close #fnum
End Sub

我这里测到a是621，之后就出现“超出文本尾”的提示框，这个问题怎么解决，代码如何改？