#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
int N,M;
vector<pair<int,int> >A;
int f()
{
	char c;
	int x,y,z;cin>>x>>y>>c>>z;
	return z+y*60+x*1440;
}
main()
{
	cin>>N>>M;
	for(int i=0;i<M;i++)
	{
		int X=f();
		A.push_back(make_pair(X,f()));
	}
	sort(A.begin(),A.end(),[](pair<int,int>a,pair<int,int>b){return a.second<b.second||a.second==b.second&&a.first<b.first;});
	vector<int>p;
	int id=0;
	for(pair<int,int>q:A)
	{
		while(id<p.size()&&p[id]<q.first)
		{
			id++;
		}
		if(id+N>p.size())
		{
			p.push_back(q.second);
		}
	}
	cout<<p.size()<<endl;
}