#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ul = unsigned long;
using ull = unsigned long long;

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int n, m;
	cin >> n >> m;

	vector<pair<int, int> > v(m);
	for (auto&& it : v)
	{
		string e[4];
		for (auto&& it2 : e)
			cin >> it2;

		it.first = stoi(e[0]) * 24 * 60 + stoi(e[1].substr(0, 2)) * 60 + stoi(e[1].substr(3, 2));
		it.second = stoi(e[2]) * 24 * 60 + stoi(e[3].substr(0, 2)) * 60 + stoi(e[3].substr(3, 2));
	}
	sort(v.begin(), v.end(),
		[](auto const& lhs, auto const& rhs)
	{
		return lhs.first < rhs.first
			|| ((lhs.first == rhs.first) && (lhs.second < rhs.second));
	});

	int res{ 0 };
	multiset<int> co;
	for (const auto& it : v)
	{
		for (auto itco = co.begin(); itco != co.end();)
		{
			if (*itco < it.first)
				itco = co.erase(itco);
			else if (*itco >= it.first)
				break;
		}

		if ((int)co.size() == n)
		{
			auto itco = --co.end();
			if (*itco > it.second)
			{
				co.erase(itco);
				co.insert(it.second);
			}
		}
		else if ((int)co.size() < n)
		{
			co.insert(it.second);
			++res;
		}
	}

	cout << res << "\n";

	return 0;
}