import java.util.*;
public class Main {
    public static void main(String... args) {
        Scanner scan=new Scanner(System.in);
        int n=scan.nextInt();
        int result=0;
        for(int i=0;i<n;i++){
            String S=scan.next();
            String t[]=S.split(":");
            S=scan.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;
            result+=k;
        }
        System.out.println(result);
    }
}