Imports System

Public Class Program

    Public Shared Sub Main(args As String())

        Dim Input As String = Console.ReadLine

        Dim cnt As Integer = 0

        For i As Integer = 0 To Math.Floor(Input.Length / 2) - 1
            If Not (Input(i) = Input(Input.Length - i - 1)) Then
                cnt += 1
            End If
        Next

        Console.WriteLine(cnt)

    End Sub
End Class