#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

bool cmp(pii a, pii b) {
    if (a.second != b.second) {
        return a.second < b.second;
    } else {
        return a.first > b.first;
    }
}

int main(){
    int N, M;
    cin >> N >> M;

    vi in(M), out(M);
    vector<pii> reserve(M);
    rep(i, M) {
        int in_d, in_h, in_m, out_d, out_h, out_m;
        char hoge;
        cin >> in_d >> in_h >> hoge >> in_m;
        cin >> out_d >> out_h >> hoge >> out_m;
        in[i] = in_m + 60 * (in_h + 24 * in_d);
        out[i] = out_m + 60 * (out_h + 24 * out_d);
        reserve[i] = mp(in[i], out[i]);
    }
    sort(all(reserve), cmp);

    vi cnt(20000);

    int ans = 0;
    each(re, reserve) {
        int l, r, ma = 0;
        tie(l, r) = re;
        for (int i = l; i <= r; ++i)smax(ma, cnt[i]);
        if (ma < N) {
            ans++;
            for (int i = l; i <= r; ++i)cnt[i]++;
        }
    }
    cout << ans << endl;
}