#include "bits/stdc++.h"
#define REP(i,n,N) for(int i=(n); i<(N); i++)
#define RREP(i,n,N) for(int i=(N-1); i>=n; i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define ALL(v) (v).begin(),(v).end()
#define p(s) cout<<(s)<<endl
#define p2(a,b) cout<<(a)<<" "<<(b)<<endl
#define v2(T) vector<vector<T>>
typedef long long ll;
using namespace std;
const ll inf=1e18+7;

int n, m;
vector<pair<int,int>> vt;
int main() {
    cin>>n>>m;
    REP(i,0,m){
        int d,hh1,mm1, o,hh2,mm2;
        scanf("%d %d:%d %d %d:%d", &d, &hh1, &mm1, &o, &hh2, &mm2);

        int in = d*24*60 + (hh1)*60 + (mm1);
        int out = o*24*60 + (hh2)*60 + (mm2);
        vt.emplace_back(in, out);
    }
    sort(ALL(vt));
    int ans=0;
    multiset<int> s;
    REP(i,0,n) s.insert(0);
    REP(i,0,m){
        auto itr = s.lower_bound(vt[i].second);
        if(itr!=s.begin()){
            itr--;
            s.erase(itr);
            s.insert(vt[i].second);
            ans++;
        }
    }
    p(ans);
    return 0;
}