import java.text.SimpleDateFormat;
import java.util.Scanner;


public class Main_yukicoder70 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

		SimpleDateFormat sdf = new SimpleDateFormat("h:m");
		int n = sc.nextInt();
		int ret = 0;
		for (int i = 0; i < n; i++) {
			try {
				String ss = sc.next();
				String ee = sc.next();
//				System.err.println(ss);
//				System.err.println(ee);
//				System.err.println(sdf.parse(ss));
//				System.err.println(sdf.parse(ee));
				long s = sdf.parse(ss).getTime();
				long e = sdf.parse(ee).getTime();
//				System.err.println(s);
//				System.err.println(e);
				ret += (Math.abs((e - s + 3600 * 24 * 1000)) % (3600 * 24 * 1000)) / 60000;
			} catch (Exception exc) {
//				throw new RuntimeException();
				sc.close();
				return;
			}
		}
        
        System.out.println(ret);
        
        sc.close();
    }
}