import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class No00000070_Main {

	public static void main(String[] args) throws IOException {

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int n = Integer.parseInt(br.readLine());

		int ans = 0;
		for(int i = 0; i < n ; i++) {
			String[] timeArr = br.readLine().split(" ");
			ans += getSleepTime(timeArr);
		}
		System.out.println(ans);
	}

	private static int getSleepTime(String[] arr) {
		int h1 = Integer.parseInt(arr[0].split(":")[0]);
		int m1 = Integer.parseInt(arr[0].split(":")[1]);
		int h2 = Integer.parseInt(arr[1].split(":")[0]);
		int m2 = Integer.parseInt(arr[1].split(":")[1]);

		if(m1 > m2) {
			h2--;
			m2 += 60;
		}
		if(h1 > h2) {
			h2 += 24;
		}
		return (h2 - h1) * 60 + (m2 - m1);
	}
}