#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

class Data
{
public:
    int in, out;
    bool operator<(const Data& d) const {
        return out < d.out;
    }
};

int main()
{
    int n, m;
    cin >> n >> m;
    vector<Data> v(m);
    for(int i=0; i<m; ++i){
        for(int j=0; j<2; ++j){
            int d, h, m;
            char tmp;
            cin >> d >> h >> tmp >> m;
            int t = (d * 24 + h) * 60 + m;
            if(j == 0)
                v[i].in = t;
            else
                v[i].out = t + 1;
        }
    }
    sort(v.begin(), v.end());

    multiset<int> ms;
    for(int i=0; i<n; ++i)
        ms.insert(0);

    int ans = 0;
    for(int i=0; i<m; ++i){
        auto it = ms.upper_bound(v[i].in);
        if(it == ms.begin())
            continue;
        -- it;
        ms.erase(it);
        ms.insert(v[i].out);
        ++ ans;
    }
    cout << ans << endl;

    return 0;
}