import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long ans = 0;
        for (int i = 0; i < n; i++) {
            int start = getTime(sc.next());
            int end = getTime(sc.next());
            ans += (end - start + 60 * 24) % (60 * 24);
        }
        System.out.println(ans);
    }
    
    static int getTime(String s) {
        String[] arr = s.split(":", 2);
        return Integer.parseInt(arr[0]) * 60 + Integer.parseInt(arr[1]);
    }
}