object Main {
  def main(args: Array[String]) {
    val sc = new java.util.Scanner(System.in)
    val n = sc.nextLine.toInt

    var ans = 0
    val re = """(\d+):(\d+) (\d+):(\d+)""".r
    for (i <- 0 to n-1) {
      val re(sh, sm, eh, em) = sc.nextLine
      val a = sh.toInt * 60 + sm.toInt
      val b = eh.toInt * 60 + em.toInt
      if (a <= b) {
        ans += b - a
      }
      else {
        ans += (24 * 60 - a) + b
      }
    }
    println(ans)
  }
}