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[] getBox = box[0].split(":");
				String[] goBox = box[1].split(":");
				int[] get = new int[2];
				int[] go = new int[2];

				for(int i = 0; i < 2; ++i){
					get[i] = Integer.parseInt(getBox[i]);
					go[i] = Integer.parseInt(goBox[i]);
				}
				int first = 0;
				int second = 0;
				if(get[1] > go[1]){
					first--;
					go[1] += 60;
				}
				second = go[1] - get[1];
				if(get[0] > go[0]){
					first += 24 - (get[0] - go[0]);
				}else{
					first += go[0] - get[0];
				}

				ans += first * 60 + second;
			}

			System.out.println(ans);

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