Getting null on getting the last record in Datagridview

Public Class frmRecords
    Private Sub frmRecords_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Dim ObjCon As New dbConnect
        ObjCon.con.Open()
        Dim da As New OleDbDataAdapter("SELECT * FROM Students", ObjCon.con)
        Dim dt As New DataTable
        da.Fill(dt)
        DataGridView1.DataSource = dt
        ObjCon.con.Close()

        Dim a As Integer = DataGridView1.Rows.Count - 1

        MessageBox.Show(DataGridView1.Rows(a).Cells(0).Value)