fun main (args : Array<String>) {
	val s = readLine()!!.toString()
	val sList : MutableList<String> = mutableListOf()
	var count : Int = 0
	for (i in s) {
		sList.add(i.toString())
	}
	for (i in 0..(sList.size - 1) / 2) {
		val p1 = i
		val p2 = (sList.size - 1) - p1
		if (sList[p1] == sList[p2]) {
			continue
		} else {
			count++
			continue
		}
	}
	println("${count}")
}