import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader stdReader =new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(stdReader.readLine());
		int hour1 = 0;
		int hour2 = 0;
		int min1 = 0;
		int min2 = 0;
		int sumhour = 0;
		int summin = 0;
		for(int i=0;i<n;i++){
			String[] temps = stdReader.readLine().split(" ");
			String[] time1 = temps[0].split(":");
			String[] time2 = temps[1].split(":");
			hour1 = Integer.parseInt(time1[0]);
			hour2 = Integer.parseInt(time2[0]);
			min1 = Integer.parseInt(time1[1]);
			min2 = Integer.parseInt(time2[1]);
			if(hour2-hour1>0){
				sumhour += hour2-hour1;
			}else if(hour2 -hour1 == 0){
				if(min2-min1 < 0){
					sumhour += 24;
				}
			}else{
					sumhour += (24+hour2)-hour1;
			}
			if(min2-min1>0){
				summin += min2-min1;
			}else{
				summin += (60+min2) - min1;
				sumhour--;
			}
		}
		System.out.println((sumhour*60+summin));
	}
}