#include <bits/stdc++.h>

using namespace std;

using Pi = pair<int, int>;

int main() {
  int n, m;
  int t[1001][2];
  scanf("%d %d", &n, &m);
  for(int i = 0; i < m; i++) {
    for(int j = 0; j < 2; j++) {
      int d, h, m;
      scanf("%d %d:%d", &d, &h, &m);
      t[i][j] = d*24*60+h*60+m;
    }
  }
  vector<Pi> vec;
  for(int i = 0; i < m; i++) {
    vec.emplace_back(t[i][0], t[i][1]);
  }
  sort(vec.begin(), vec.end());
  int room[101] = {};
  vector<int> who;
  int ans = 0;
  auto print = [&](int ts) {
    printf("%d %d:%d\n", ts/(24*60), ts%(24*60)/60, ts%(24*60)%60);
  };
  function<void(int,int)> dfs = [&](int idx, int cnt) {
    if(idx == m) {
      ans = max(ans, cnt);
      /*
      if(cnt == 11) {
	for(int s : who) {
	  print(s);
	}
	exit(0);
      }
      */
      return;
    }
    dfs(idx+1, cnt);
    for(int i = 0; i < n; i++) {
      if(room[i] < vec[idx].first) {
	int tmp = room[i];
	room[i] = vec[idx].second;
	who.push_back(vec[idx].second);
	dfs(idx+1, cnt+1);
	who.pop_back();
	room[i] = tmp;
      }
    }
  };
  dfs(0, 0);
  printf("%d\n", ans);

  return 0;
}