import java.util.Scanner;

public class Main70 {
	public static void main(String[] args) {
		Main70 p = new Main70();
	}

	public Main70() {
		solve();
	}

	public void solve() {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		
		int total = 0;
		for(int i=0;i<n;i++){
			String[] s = (sc.next()+":" + sc.next()).split(":");
			int st = Integer.parseInt(s[0])*60 + Integer.parseInt(s[1]);
			int en = Integer.parseInt(s[2])*60 + Integer.parseInt(s[3]);
			
			if(st>en)
				total += (24*60 - st) + en;
			else
				total += (en-st);
		}
		
		System.out.println(total);
		
	}

}