import io.StdIn.{readInt, readLine}
object Main extends App {
  val n = readInt
  val a = readLine
  val b = readLine
  val c = readLine

  val diff_count = (0 until n).map(i => {
    val chA = a(i)
    val chB = b(i)
    val chC = c(i)
    
    if      (chA == chB && chB == chC && chC == chA) 0
    else if (chA == chB && chB != chC && chC != chA) 1
    else if (chA != chB && chB == chC && chC != chA) 1
    else if (chA != chB && chB != chC && chC == chA) 1
    else  /*(chA != chB && chB != chC && chC != chA)*/ 2

  }).sum
  println(diff_count)
}