#include<stdio.h>
#include<queue>
#include<map>
#include<iostream>

struct E{
	int i,o;
	bool operator<(const E& e1)const{
		if(o!=e1.o)return o>e1.o;
		return i>e1.i;
	}
};



int main(){
	std::priority_queue<E> pq;
	std::map<int,int> ms;
	int n,m;
	scanf("%d %d",&n,&m);
	for(int i=0;i<m;i++){
		int d1,d2,h1,h2,m1,m2;
		scanf("%d %d:%d %d %d:%d",&d1,&h1,&m1,&d2,&h2,&m2);
		E e1;
		e1.i=d1*10000+h1*100+m1;
		e1.o=d2*10000+h2*100+m2;
		pq.push(e1);
		if(e1.i>=e1.o){
			printf("err\n");
		}
		//std::cout<<d1<<" "<<h1<<" "<<m1<<" "<<d2<<" "<<h2<<" "<<m2<<"\n";
	}
	int count=0,ans=0;
	while(pq.empty()==false){
		E e1=pq.top();
		pq.pop();
		std::map<int,int>::iterator it=ms.begin();
		while((it!=ms.end())&&((*it).first<e1.i)){
			int add=(*it).second;
			count-=add;
			ans+=add;
			ms.erase(it);
			it=ms.begin();
		}
		
		if(count>=n){
			ms[e1.o]++;
			count++;
			if(count>n){
				it=ms.end();
				it--;
				(*it).second--;
				if((*it).second<1){
					ms.erase(it);
				}
				count--;
			}
		}else{
			count++;
			ms[e1.o]++;
		}
	}
	ans+=count;
	printf("%d\n",ans);
}