import java.util.Scanner;

class Main{
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		while(sc.hasNext()){
			int n=sc.nextInt();
			int sum=0;
			for(int i=0;i<n;i++){
				String[] s1=(sc.next()).split(":");
				String[] s2=(sc.next()).split(":");
				int t1=24*60-Integer.valueOf(s1[0])*60-Integer.valueOf(s1[1]);
				int t2=Integer.parseInt(s2[0])*60+Integer.valueOf(s2[1]);
				if(t1>12*60) t1=-Integer.valueOf(s1[0])*60-Integer.valueOf(s1[1]);
				if(t2>12*60) t2=Integer.valueOf(s2[0])*60+Integer.valueOf(s2[1])-24*60;
				sum+=t1+t2;
			}
			System.out.println(sum);
		}
	}
}