package m.shin;
import java.util.Scanner;
public class Con70 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int N = s.nextInt();
		String[] start = new String[N];
		String[] end = new String[N];
		 for(int i = 0;i < N;i++){
			 start[i] = s.next();
			 end[i] = s.next();
		 }
		 s.close();

		 int count = 0;
		 for(int i = 0;i < N;i++){
			 int a = Integer.parseInt(start[i].substring(0, start[i].indexOf(":"))) * 60 + Integer.parseInt(start[i].substring(start[i].indexOf(":") + 1,start[i].length()));
			 int b = Integer.parseInt(end[i].substring(0, end[i].indexOf(":"))) * 60 + Integer.parseInt(end[i].substring(end[i].indexOf(":") + 1,end[i].length()));
			 count += b-a;
			 if(a > b){
				 count += 24 * 60;
			 }
		 }
		 System.out.println(count);

	}

}