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 S=sc.next();
			String t[]=S.split(":");
			S=sc.next();
			String u[]=S.split(":");
			int k=Integer.valueOf(u[0])*60+Integer.valueOf(u[1])-Integer.valueOf(t[0])*60-Integer.valueOf(t[1]);
			if(k<0)k=1440+k;
			ans+=k;
		}
		System.out.println(ans);
	}}