fun main(args: Array<String>) {

    val s = readLine()!!
    val s2 = s.substring(0, s.length/2)
    val s3 = s.reversed().substring(0, s.length/2)
    var cnt = 0

    for(i in 0 until s.length/2) {
        if(s2[i] != s3[i]) {
            cnt++
        }
    }
    println(cnt)
}