import java.util.Scanner

object Main {
  def main(args: Array[String]) {
    val result = solve(new Scanner(System.in))
    if (result.length > 0) println(result)
  }

  def solve(in: String): String = solve(new Scanner(in))

  def solve(sc: Scanner): String = {
    val S = sc.next

    var ans = 0
    for (i <- 0 until S.length / 2) {
      if (S(i) != S(S.length - i - 1)) {
        ans += 1
      }
    }
    ans.toString
  }
}
