import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.next());

        int sumHour[] = {0};
        int sumMin[]  = {0};


        for (int i = 0; i < N; i++) {
            String G = sc.next();
            String W = sc.next();

            int Gh = Integer.parseInt(G.split(":")[0]);
            int Gm = Integer.parseInt(G.split(":")[1]);
            int Wh = Integer.parseInt(W.split(":")[0]);
            int Wm = Integer.parseInt(W.split(":")[1]);

            if (Wh - Gh < 0) {
                sumHour[0] += ((24 - Gh) + Wh) - 1;
            } else {
                sumHour[0] += Wh - Gh - 1;
            }
            sumMin[0] += 60 - Gm + Wm;

            sumHour[0] += sumMin[0] / 60;
            sumMin[0] %= 60;
        }
        System.out.println(sumHour[0]*60 + sumMin[0]);
    }
}