package yukicoder;

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

public class Main {
	public static void main(String[] args) {
		BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));

		try {
			int count = Integer.parseInt(buff.readLine());
			int ans = 0;
			while (count-- > 0) {
				String[] box = buff.readLine().split(" ");
				String[] goBox = box[0].split(":");
				String[] getBox = box[1].split(":");
				int go = 0;
				int get = 0;

				for (int i = 0; i < 2; ++i) {
					int mul = 1;
					if (i == 0) {
						mul = 60;
					}
					get += Integer.parseInt(getBox[i]) * mul;
					go += Integer.parseInt(goBox[i]) * mul;
				}
				if (get - go > 0) {
					ans += get - go;
				} else {
					ans += 24 * 60 - Math.abs(get - go);
				}
			}
			System.out.println(ans);

		} catch (NumberFormatException e) {
			e.getStackTrace();
		} catch (IOException e) {
			e.getStackTrace();
		} catch (Exception e) {
			e.getStackTrace();
		}
	}
}