#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

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

  vector<pair<int, int> > ts(m);
  for (int i = 0; i < m; i++) {
    int d1, h1, m1, d2, h2, m2;
    char _;
    cin >> d1 >> h1 >> _ >> m1 >> d2 >> h2 >> _ >> m2;
    int in = 60 * (24 * d1 + h1) + m1;
    int out = 60 * (24 * d2 + h2) + m2;
    ts[i] = make_pair(out, in);
  }

  sort(ts.begin(), ts.end());
  
  int ret = 0;
  queue<int> q;
  for (int i = 0; i < m; i++) {
    int in, out;
    tie(out, in) = ts[i];
    while (!q.empty() && q.front() < in) {
      q.pop();
    }
    if (q.size() < n) {
      ++ret;
      q.push(ts[i].first);
    }
  }
  
  cout << ret << endl;
  return 0;
}