#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
const int mod = 1e9 + 7;
const int maxn = 200005;
const int inf = 1e9;
int tiempo[maxn], x[maxn], y[maxn], pref[maxn], dp[maxn];
void solve() {
  int r, n;
  cin >> r >> n;
  for (int i = 1; i <= n; i++) {
    cin >> tiempo[i] >> x[i] >> y[i];
    dp[i] = -inf;
  }
  x[0] = y[0] = 1;
  int ans = -inf;
  for (int i = 1; i <= n; i++) {
    for (int j = i - 1; j >= 0; j--) {
      if (tiempo[i] - tiempo[j] > 2 * r) {
        dp[i] = max(dp[i], pref[j] + 1);
        break;
      }
      int dist = abs(x[i] - x[j]) + abs(y[i] - y[j]);
      if (dist <= (tiempo[i] - tiempo[j])) {
        dp[i] = max(dp[i], dp[j] + 1);
      }
    }
    pref[i] = pref[i - 1];
    pref[i] = max(pref[i], dp[i]);
    ans = max(ans, pref[i]);
  }
  cout << ans << '\n';
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
