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

#define REP(i,n) for(int i=0;i<(n);i++)
#define ALL(v) v.begin(),v.end()

typedef pair<int,int> P;

signed main(){
  int n,m;cin>>n>>m;
  vector<P> v(m);
  REP(i,m){
    int d,h,mi;char c;
    cin>>d>>h>>c>>mi;
    v[i].second=(d*24+h)*60+mi;
    cin>>d>>h>>c>>mi;
    v[i].first=(d*24+h)*60+mi;
  }
  sort(ALL(v));
  multiset<int> s;
  REP(i,n)s.insert(0);
  int ans=0;
  REP(i,m){
    int en=v[i].first,be=v[i].second;
    if(*s.begin()>=be)continue;
    s.erase(--s.lower_bound(be));
    s.insert(en);
    ans++;
  }
  cout<<ans<<endl;
}