import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Test2{
	public static void main(String[] args) {
		try{
			BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
			int N = Integer.parseInt(br.readLine());
			System.out.println(CalcTime(br, N));
		}
		catch(IOException e){
			e.getStackTrace();
		}
		catch(NumberFormatException e){
			e.getStackTrace();
		}
	}
	
	public static long CalcTime(BufferedReader br, int n) throws IOException{
		int ans = 0;
		for(int i=0; i< n; i++){
			String[] str = br.readLine().split(" ");
			SimpleDateFormat sdf = new SimpleDateFormat("HH:mm");
			Date timeTo =new Date();
			Date timeFrom = new Date();
			try{
				timeFrom = sdf.parse(str[0]);
				timeTo = sdf.parse(str[1]);
			}catch(ParseException e){
				e.getStackTrace();
			}
			long timeFrom1 = timeFrom.getTime();
			long timeTo1 = timeTo.getTime();
			long timeDiff = (timeTo1 - timeFrom1) / (1000*60);
			if(timeDiff < 0 ) timeDiff += 1440;
			
			ans += timeDiff;
		}
		return ans;
	}
}