import java.util.Scanner;

public class pre {
    public static void main(String[] args) {

        Scanner s = new Scanner(System.in);
		int n = s.nextInt(),sum = 0,H,M,h,m;
		
		for(int i=0;i<n;i++){
			String[] time = s.next().split(":");
			
			H = Integer.parseInt(time[0]);
			M = Integer.parseInt(time[1]);
			
			time = s.next().split(":");
			
			h = Integer.parseInt(time[0]);
			m = Integer.parseInt(time[1]);
			
			if(h==H && M>m){
				sum = sum + (60-M) + 23*60 + m;
			}
			else if(h==H && M<m){
				sum = sum + (m - M);
			}
			else if((h - H) < 0){
				sum = sum + (((24+h)*60+m) - (H*60+M));
			}
			else{
				sum = sum + ((h*60+m) - (H*60+M));
			}
	    }
		
		System.out.println(sum);
    }
}