#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N,M;

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>M;
	vector<pair<int,int>> V;
	FOR(i,M) {
		char cc;
		int a,b,c;
		cin>>a>>b>>cc>>c;;
		x=a*24*60+b*60+c;
		cin>>a>>b>>cc>>c;;
		y=a*24*60+b*60+c+1;
		V.push_back({y,x});
	}
	
	sort(ALL(V));
	multiset<int> R;
	FOR(i,N) R.insert(-1);
	int ret=0;
	FORR(v,V) {
		auto it=R.lower_bound(v.second+1);
		if(it!=R.begin()) {
			it--;
			ret++;
			R.erase(it);
			R.insert(v.first);
		}
	}
	cout<<ret<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}