How do I keep track of the last folder selected by a user?

I thought using application settings would do the trick but I'm not getting it to work. This is what I have:

private void btnBrowse_Click(object sender, EventArgs e)
        {
            if (fbFolderBrowser.ShowDialog() == DialogResult.OK)
            {
                // I want to open the last folder selected by the user here.
            }

When the user clicks on this button, I want to open the browse window to the last folder he accessed and save it. Next time he clicks on the button, it'll automatically select that folder.

I was thinking maybe I could use user variables where I can change at run-time but I'm not getting it to work. Can anyone give me a hand?