import java.util.Scanner;
class N070{
	public static void main(String args[]){
		Scanner s = new Scanner(System.in);
		int n = s.nextInt();
		int sum = 0;
		for(int i = 0; i < n; i++){
			String a = s.next();
			String b = s.next();
			String a1[] = a.split(":");
			String b1[] = b.split(":");
			int a2 = Integer.parseInt(a1[0]) * 60 + Integer.parseInt(a1[1]);
			int b2 = Integer.parseInt(b1[0]) * 60 + Integer.parseInt(b1[1]);
			if(b2 >= a2){
				sum += b2 - a2;
			}else{
				sum += b2 - a2 + 1440;
			}
		}
		System.out.println(sum);
	}
}