Option Strict On

Module Module1

    Sub Main()
        'let'
        Dim N As Long = CLng(Console.ReadLine())

        'var'
        Dim ans As String

        If N < CLng(10 ^ 3) Then
            ans = "ABC"
        Else
            ans = "ABD"
        End If

        Console.WriteLine(ans)

    End Sub
End Module