import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int ans = 0;
    for(int i = 0; i < N; i++) {
      String sleep = sc.next();
      String wake = sc.next();
      String[] s = sleep.split(":");
      String[] w = wake.split(":");
      int H = Integer.parseInt(s[0]);
      int M = Integer.parseInt(s[1]);
      int h = Integer.parseInt(w[0]);
      int m = Integer.parseInt(w[1]);
      int sleepT = 60 * H + M;
      int wakeT = 60 * h + m;
      if(wakeT >= sleepT) {
        ans += (wakeT - sleepT);
      } else {
        ans += (60 * 24 - (sleepT - wakeT));
      }
    }
    System.out.println(ans);
  }
}