import java.io.*;
import java.util.*;
import java.math.*;

class Main {
	
	public static void out (Object o) {
		System.out.println(o);
	}
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		int n = Integer.parseInt(br.readLine());
		int ans = 0;
		
		for (int i = 0; i < n; i++) {
			String[] line = br.readLine().split(" ");
			String[] time1 = line[0].split(":");
			String[] time2 = line[1].split(":");
			int h1 = Integer.parseInt(time1[0]);
			int m1 = Integer.parseInt(time1[1]);
			int h2 = Integer.parseInt(time2[0]);
			int m2 = Integer.parseInt(time2[1]);
			int t1 = h1 * 60 + m1;
			int t2 = h2 * 60 + m2;
			ans += t1 <= t2 ? t2 - t1 : 1440 - (t1 - t2);
		}
		
		out(ans);
	}
}