#include <bits/stdc++.h>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(a);i>=(b);i--)
#define pb push_back
#define pcnt __builtin_popcount
#define show(x) cout<<#x<<" = "<<x<<endl;
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define fi first
#define se second
#define rng(a) a.begin(),a.end()
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define sz(x) (int)(x).size()
#define mp make_pair

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
typedef set<int> si;
typedef pair<ll,ll> pll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<pll> vpll;
typedef set<ll> sl;
template<typename T>string join(vector<T>&v)
{stringstream s;FOR(i,0,sz(v))s<<' '<<v[i];return s.str().substr(1);}
ll gcd(ll a,ll b){if(a>b)swap(a,b);for(;a>0;b%=a,swap(a,b));return b;}
int modpow(ll a,ll n,int m){if(a==0)return a;ll p=1;for(;n>0;n/=2,a=a*a%m)if(n&1)p=p*a%m;return(int)p;}
void dout(double d){printf("%.12f\n",d);}

const int iinf = 1e9;
const ll linf = 1e18;
const int mod = 1e9+7;
const double pi = acos(-1);
const double eps = 1e-10;

string s;
int n, m;
int get_time(){
  int d, h, m;
  cin >> d >> s;
  h = (s[0] - '0') * 10 + (s[1] - '0');
  m = (s[3] - '0') * 10 + (s[4] - '0');
  return (d * 24 + h) * 60 + m - 2880;
}
vpii cl;
map<int, int> ts;
int im[2005];
main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> n >> m;
  FOR(i, 0, m){
    int tin = get_time(), tout = get_time();
    if(tin < 0 || 10080 <= tout)continue;
    ts[tin] = 0;
    ts[tout] = 0;
    cl.pb(pii(tout, -tin));
  }
  sort(rng(cl));
  int tcnt=0;
  each(itr, ts){
    ts[itr->fi] = tcnt;
    tcnt++;
  }

  int ans = 0;
  each(itr, cl){
    int tin = ts[-itr->se], tout = ts[itr->fi]+1;
    bool z = true;
    ll s = 0;
    FOR(i, 0, tin) s += im[i];
    FOR(i, tin, tout){
      s += im[i];
      if(s >= n){
        z = false;
        break;
      }
    }
    if(z){
      im[tin]++;
      im[tout]--;
      ans++;
    }
  }
  cout << ans << endl;
  return 0;
}