Class Program
    Shared Sub Main(args As String())
        Dim s As String = Console.ReadLine()
        Dim t As String = Console.ReadLine()
        Dim arrS As Char() = s.ToCharArray()
        Dim arrT As Char() = t.ToCharArray()
        Dim cnt As Integer = arrS.Length
        Dim diff As Integer = 0
        For i As Integer = 0 To cnt - 1
            If Not arrS(i).Equals(arrT(i)) Then diff += 1
        Next
        Console.WriteLine(diff)
    End Sub
End Class