//No.70 睡眠の重要性！

import java.util.*;
import java.io.*;
import static java.util.Arrays.*;
import static java.lang.Math.*;

public class No70 {

    static final InputStream in = System.in;
    static final PrintWriter out = new PrintWriter(System.out,false);

    static void solve() throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        int ans = 0;
        while (n-- > 0) {
            String[] input = br.readLine().split(" ");
            int h1 = Integer.parseInt(input[0].split(":")[0]);
            int m1 = Integer.parseInt(input[0].split(":")[1]);
            int h2 = Integer.parseInt(input[1].split(":")[0]);
            int m2 = Integer.parseInt(input[1].split(":")[1]);
            if (h1 >= h2) {
                if (m1 >= m2) {
                    ans += (24-h1+h2-1)*60 + 60-(m1-m2);
                }else {
                    ans += (24-h1+h2)*60 + (m2-m1);
                }
            }else {
                if (m1 >= m2) {
                    ans += (h2-h1-1)*60 + 60-(m1-m2);
                }else {
                    ans += (h2-h1)*60 + (m2-m1);
                }
            }
        }
        out.println(ans);
    }

    public static void main(String[] args) throws Exception {
        long start = System.currentTimeMillis();

        solve();
        out.flush();

        long end = System.currentTimeMillis();
        //trace(end-start + "ms");
        in.close();
    }

    static void trace(Object... o) { System.out.println(deepToString(o));}
}