#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);
    vi times;
    rep(i, M) {
        int in_d, in_h, in_m, out_d, out_h, out_m;
        scanf("%d %d:%d", &in_d, &in_h, &in_m);
        scanf("%d %d:%d", &out_d, &out_h, &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]);
        times.push_back(in[i]);
        times.push_back(out[i]);
    }
    sort(all(times));
    times.erase(unique(all(times)), times.end());
    sort(all(reserve), cmp);

    int T = sz(times);

    auto lb = [&](int x) {
        return lower_bound(all(times), x) - times.begin();
    };
    vi cnt(T);

    int ans = 0;
    each(re, reserve) {
        int l = lb(re.first), r = lb(re.second);
        int ma = 0;
        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;
}