import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int total =0;
        for(int i=0; i<N; i++){
            String S = sc.next();
            String [] arr1 = S.split(":");
            S = sc.next();
            String [] arr2 = S.split(":");
            int H = Integer.parseInt(arr1[0]);
            int M = Integer.parseInt(arr1[1]);
            int h = Integer.parseInt(arr2[0]);
            int m = Integer.parseInt(arr2[1]);
            int a = h-H;
            int b = m-M;
            if(b<0){
                a=a-1;
                b=b+60;
            }
            if(a<0){
                a = a +24;
            }
            int z = a*60+b;
            total = total + z;
        }
        System.out.println(total);
    }
}