#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N, M;
	cin >> N >> M;
	vector<int> L(M), R(M);
	REP(i, M) {
		int d[2], h[2], m[2];
		scanf("%d %d:%d %d %d:%d", d, h, m, d + 1, h + 1, m + 1);
		auto conv = [](int d, int h, int m) {
			return (d - 2) * 24 * 60 + h * 60 + m;
		};
		L[i] = conv(d[0], h[0], m[0]);
		R[i] = conv(d[1], h[1], m[1]) + 1;
	}
	
	vector<int> ord(M);
	iota(ALL(ord), 0);
	sort(ALL(ord), [&](int i, int j) { return L[i] < L[j]; });
	
	multiset<int> ms; // 最小の R
	REP(i, N) ms.insert(INF);
	int ans = 0;
	for (int i : ord) {
		while (!ms.empty() && *ms.begin() <= L[i]) {
			ms.erase(ms.begin());
			ms.insert(INF);
			++ans;
		}
		if (*--ms.end() > R[i]) {
			ms.erase(--ms.end());
			ms.insert(R[i]);
		}
	}
	while (!ms.empty() && *ms.begin() != INF) {
		ms.erase(ms.begin());
		++ans;
	}
	cout << ans << endl;
}