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 N = sc.nextInt
    sc.nextLine
    val ABC = Array.fill(3)(sc.nextLine)

    var n = 0
    for (i <- 0 until N) {
      if (ABC(0)(i) != ABC(1)(i)) {
        n += 1
      }
      if (ABC(0)(i) != ABC(2)(i) && ABC(1)(i) != ABC(2)(i)) {
        n += 1
      }
    }
    n.toString
  }
}
