import java.util.*;
import java.math.*;
import java.io.*;
 
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int sum = 0;
		for(int i = 0; i < N; i++) {
			String[] st = sc.next().split(":");
			String[] en = sc.next().split(":");
			int sth = Integer.parseInt(st[0]);
			int stm = Integer.parseInt(st[1]);
			int enh = Integer.parseInt(en[0]);
			int enm = Integer.parseInt(en[1]);
			if(enh < sth) enh += 24;
			int plus = (enh * 60 + enm ) - (sth * 60 + stm);
			sum += plus;
		}
		System.out.println(sum);
	}
}