open System
let R T = stdin.ReadLine()|> T
let RS T = stdin.ReadLine().Split()|>Array.map T
let Mod = (1e9|>int64)+7L
[<EntryPoint>]
let main argv =
    let S = R string
    [0..(S.Length/2 - 1)]
    |>Seq.sumBy(fun c -> if (S.[c]=S.[S.Length-1-c]) then 0 else 1)
    |>stdout.WriteLine
    0
