Option Strict On
Module ProblemB

    Sub Main()
        Dim s() As Char = Console.ReadLine.ToCharArray()
        Dim i, j As Integer
        Dim ans As Integer = 0

        For i = 0 To s.Length - 1
            j = s.Length - i - 1
            If s(i) <> s(j) Then
                ans += 1
            End If
            If i = j OrElse i + 1 = j Then Exit For
        Next

        Console.WriteLine(ans.ToString)
    End Sub

End Module