import java.util.*;
 

public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n= sc.nextInt();
		int ans=0;
		for(int i=0;i<n;i++){
			String a = sc.next();
			String[] aa=a.split("//s|:");
			String ab = sc.next();
			String[] bb =ab.split("//s|:");
			int s =Integer.parseInt(aa[0])*60+Integer.parseInt(aa[1]);
			int t =Integer.parseInt(bb[0])*60+Integer.parseInt(bb[1]);
			if(s>t) t+=24*60;
			ans+=(t-s);
		}
		System.out.println(ans);
	}
}