import java.util.Scanner;

public class No70 {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		//計測する日数
		int n =scan.nextInt();
		//寝た時間の合計
		int sum = 0;
		//寝た時間を計測
		for(int i=0;i<n;i++){
			String hi = scan.next();
			String ho = scan.next();
			String[] in = hi.split(":");
			String[] out = ho.split(":");
			int time1 = Integer.parseInt(in[0])*60+Integer.parseInt(in[1]);
			int time2 = Integer.parseInt(out[0])*60+Integer.parseInt(out[1]);
			if(time2-time1<0){
				time2 += 24*60;
			}
			sum += time2-time1;
		}
		//寝た時間の合計を出力
		System.out.println(sum);
	}
}