import java.util.Scanner;
	

public class Main{
	
	
	public static void main(String args[])throws Exception{
		
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int ans = 0;
		for(int i=0;i<N;i++){
			String A = sc.next();
			String B = sc.next();
			int basyoA = colon(A);
			int basyoB = colon(B);
			String HH = A.substring(0,basyoA);
			String MM = A.substring(basyoA+1);
			int H = Integer.parseInt(HH);
			int M = Integer.parseInt(MM);
			int timeA = H*60+M;
			String hh = B.substring(0,basyoB);
			String mm = B.substring(basyoB+1);
			int h = Integer.parseInt(hh);
			int m = Integer.parseInt(mm);
			int timeB = h*60+m+1440;
			ans += (timeB-timeA)%1440;
		}
		System.out.println(ans);
	}

	private static int colon(String a) {
		for(int i=0;i<a.length();i++){
			if(a.charAt(i) == ':'){
				return i;
			}
		}
		return 0;
		
	}
}