import java.util.*;
import java.io.*;

public class Main {
	public static void main (String[] args) throws Exception {
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String[] first = br.readLine().split(" ", 2);
		int m = Integer.parseInt(first[0]);
		int n = Integer.parseInt(first[1]);
		ArrayList<Customer> list = new ArrayList<>();
		for (int i = 0; i < n; i++) {
		    list.add(new Customer(i, br.readLine()));
		}
		Collections.sort(list, new Comparator<Customer>() {
		    public int compare(Customer c1, Customer c2) {
		        if (c1.left == c2.left) {
		            return c1.right - c2.right;
		        } else {
		            return c1.left - c2.left;
		        }
		    }
		});
		TreeSet<Customer> stays = new TreeSet<>();
		int count = 0;
		for (Customer c : list) {
		    while (stays.size() > 0 && stays.first().right < c.left) {
		        stays.pollFirst();
		    }
		    stays.add(c);
		    if (stays.size() > m) {
		        count++;
		        stays.pollLast();
		    }
		}
		System.out.println(n - count);
    }
    
    static class Customer implements Comparable<Customer> {
        int idx;
        int left;
        int right;
        
        public Customer(int idx, String line) {
            this.idx = idx;
            String[] args = line.split(" ", 4);
            left = Integer.parseInt(args[0]) * 24 * 60;
            String[] in = args[1].split(":", 2);
            left += Integer.parseInt(in[0]) * 60;
            left += Integer.parseInt(in[1]);
            right = Integer.parseInt(args[2]) * 24 * 60;
            String[] out = args[3].split(":", 2);
            right += Integer.parseInt(out[0]) * 60;
            right += Integer.parseInt(out[1]);
        }
        
        public int hashCode() {
            return idx;
        }
        
        public int compareTo(Customer another) {
            if (right == another.right) {
                return idx - another.idx;
            } else {
                return right - another.right;
            }
        }
    }
}