import scala.math.ceil

object Main {
  val sc = new java.util.Scanner(System.in)

  def sin(n: Int): Seq[Int] = Seq.fill(n)(sc.nextInt())

  def iin(): Int = sc.nextLine().toInt

  def main(args: Array[String]): Unit = {
    val n = iin()
    val s = Seq.fill(3)(sc.nextLine())

    var cnt = 0;
    for(i <- 0 until n){
      val size = Set(s(0)(i), s(1)(i), s(2)(i)).size
      cnt += size - 1
    }
    println(cnt)
  }
}