#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;
    }
  }
  priority_queue<Pi, vector<Pi>, greater<Pi>> que;
  for(int i = 0; i < m; i++) {
    que.emplace(t[i][1], t[i][0]);
  }
  int room[101] = {};
  int ans = 0;
  auto print = [&](int ts) {
    printf("%d %d:%d\n", ts/(24*60), ts%(24*60)/60, ts%(24*60)%60);
  };
  while(!que.empty()) {
    Pi p = que.top(); que.pop();
    int idx = -1;
    for(int i = 0; i < n; i++) {
      if(room[i] >= p.second) continue;
      if(idx == -1 || room[idx] < room[i]) idx = i;
    }
    if(~idx) {
      ans++;
      room[idx] = p.first;
      //print(p.first);
    }
  }
  printf("%d\n", ans);

  return 0;
}