#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;

struct SegTree{
  typedef int T;
  T e = 0;
  T m(const T&a, const T&b){return a + b;}
//###################################################
  typedef int i;i n;vector<T> d;
  void init(i m){n=1<<(32-__builtin_clz(m-1));d.resize(2*n-1);FOR(j,0,2*n-1)d[j]=e;}
  void init(vector<T>&v){n=1<<(32-__builtin_clz(sz(v)-1));d.resize(2*n-1);FOR(j,0,sz(v))d[j+n-1]=v[j];FORR(k, n-2, 0)d[k]=m(d[k*2+1],d[k*2+2]);}
  void update(i k,T a){k+=n-1;d[k]=a;while(k>0){k=(k-1)/2;d[k]=m(d[k*2+1],d[k*2+2]);}}
  T q(i a,i b,i k,i l,i r){return (r<=a||b<=l)?e:(a<=l&&r<=b)?d[k]:m(q(a,b,k*2+1,l,(l+r)/2),q(a,b,k*2+2,(l+r)/2,r));}
  T query(i a,i b){return q(a,b,0,0,n);}
};

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;
    cl.pb(pii(tout, -tin));
  }
  sort(rng(cl));
  SegTree seg;
  seg.init(10100);
  int ans = 0;
  each(itr, cl){
    int tin = -itr->se, tout = itr->fi;
    tout++;
    if(seg.query(0, tin+1) < n){
      seg.update(tin, seg.query(tin, tin+1) + 1);
      seg.update(tout, seg.query(tout, tout+1) - 1);
      ans++;
    }
  }
  cout << ans << endl;
  return 0;
}