#include <bits/stdc++.h>
using namespace std;

const int MAXN = 100;
const int MAXM = 1000;

int N, M;
int S[MAXM], T[MAXM];
int tord[MAXM];

signed main() {
  ios::sync_with_stdio(false);
  cin >> N >> M;
  for (int i = 0; i < M; ++i) {
    int d, h, m;
    char c;
    cin >> d >> h >> c >> m;
    S[i] = d * 24 * 60 + h * 60 + m;
    cin >> d >> h >> c >> m;
    T[i] = d * 24 * 60 + h * 60 + m + 1;
    tord[i] = i;
  }
  sort(tord, tord + M, [&] (int i, int j) { return T[i] < T[j]; });
  multiset<int> bag;
  for (int i = 0; i < N; ++i) {
    bag.emplace(-1);
  }
  int ans = 0;
  for (int i = 0; i < M; ++i) {
    auto it = bag.upper_bound(S[tord[i]]);
    if (it == bag.begin()) continue;
    ++ans;
    bag.erase(--it);
    bag.emplace(T[tord[i]]);
  }
  cout << ans << endl;
  return 0;
}