import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader stdReader =new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(stdReader.readLine());
		int sum1 = 0;
		int sum2 = 0;
		int sum = 0;
		for(int i=0;i<n;i++){
			String[] temps = stdReader.readLine().split(" ");
			String[] time1 = temps[0].split(":");
			String[] time2 = temps[1].split(":");
			sum1 = Integer.parseInt(time1[0])*60+Integer.parseInt(time1[1]);
			sum2 = Integer.parseInt(time2[0])*60+Integer.parseInt(time2[1]);			
			if(sum2 - sum1 < 0)sum2+=24*60;
			sum += sum2-sum1;
		}
		System.out.println(sum);
	}
}