fun main(args: Array<String>) {
    val s = readLine()!!
    val left = s.substring(0 until s.length / 2)
    val right = s.reversed().substring(0 until s.length / 2)

    var sum = 0
    for (i in left.indices) {
        if (left[i] != right[i]) {
            sum++
        }
    }
    println(sum)
}


