#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e8;
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...);
}
static struct FastInput {
  static constexpr int BUF_SIZE = 1 << 20;
  char buf[BUF_SIZE];
  size_t chars_read = 0;
  size_t buf_pos = 0;
  FILE* in = stdin;
  char cur = 0;
  inline char get_char() {
    if (buf_pos >= chars_read) {
      chars_read = fread(buf, 1, BUF_SIZE, in);
      buf_pos = 0;
      buf[0] = (chars_read == 0 ? -1 : buf[0]);
    }
    return cur = buf[buf_pos++];
  }
  inline void tie(int) {}
  inline explicit operator bool() { return cur != -1; }
  inline static bool is_blank(char c) { return c <= ' '; }
  inline bool skip_blanks() {
    while (is_blank(cur) && cur != -1) {
      get_char();
    }
    return cur != -1;
  }
  inline FastInput& operator>>(char& c) {
    skip_blanks();
    c = cur;
    return *this;
  }
  inline FastInput& operator>>(string& s) {
    if (skip_blanks()) {
      s.clear();
      do {
        s += cur;
      } while (!is_blank(get_char()));
    }
    return *this;
  }
  template <typename T>
  inline FastInput& read_integer(T& n) {
    n = 0;
    if (skip_blanks()) {
      int sign = +1;
      if (cur == '-') {
        sign = -1;
        get_char();
      }
      do {
        n += n + (n << 3) + cur - '0';
      } while (!is_blank(get_char()));
      n *= sign;
    }
    return *this;
  }
  template <typename T>
  inline typename enable_if<is_integral<T>::value, FastInput&>::type operator>>(
      T& n) {
    return read_integer(n);
  }
  inline FastInput& operator>>(__int128& n) { return read_integer(n); }
  template <typename T>
  inline typename enable_if<is_floating_point<T>::value, FastInput&>::type
  operator>>(T& n) {
    n = 0;
    if (skip_blanks()) {
      string s;
      (*this) >> s;
      sscanf(s.c_str(), "%lf", &n);
    }
    return *this;
  }
} fast_input;
static struct FastOutput {
  static constexpr int BUF_SIZE = 1 << 20;
  char buf[BUF_SIZE];
  size_t buf_pos = 0;
  static constexpr int TMP_SIZE = 1 << 20;
  char tmp[TMP_SIZE];
  FILE* out = stdout;
  inline void put_char(char c) {
    buf[buf_pos++] = c;
    if (buf_pos == BUF_SIZE) {
      fwrite(buf, 1, buf_pos, out);
      buf_pos = 0;
    }
  }
  ~FastOutput() { fwrite(buf, 1, buf_pos, out); }
  inline FastOutput& operator<<(char c) {
    put_char(c);
    return *this;
  }
  inline FastOutput& operator<<(const char* s) {
    while (*s) {
      put_char(*s++);
    }
    return *this;
  }
  inline FastOutput& operator<<(const string& s) {
    for (int i = 0; i < (int)s.size(); i++) {
      put_char(s[i]);
    }
    return *this;
  }
  template <typename T>
  inline char* integer_to_string(T n) {
    char* p = tmp + TMP_SIZE - 1;
    if (n == 0) {
      *--p = '0';
    } else {
      bool is_negative = false;
      if (n < 0) {
        is_negative = true;
        n = -n;
      }
      while (n > 0) {
        *--p = (char)('0' + n % 10);
        n /= 10;
      }
      if (is_negative) {
        *--p = '-';
      }
    }
    return p;
  }
  template <typename T>
  inline typename enable_if<is_integral<T>::value, char*>::type stringify(T n) {
    return integer_to_string(n);
  }
  inline char* stringify(__int128 n) { return integer_to_string(n); }
  template <typename T>
  inline typename enable_if<is_floating_point<T>::value, char*>::type stringify(
      T n) {
    sprintf(tmp, "%.17f", n);
    return tmp;
  }
  template <typename T>
  inline FastOutput& operator<<(const T& n) {
    auto p = stringify(n);
    for (; *p != 0; p++) {
      put_char(*p);
    }
    return *this;
  }
} fast_output;
const int maxn = 1e5 + 5;
int r, n;
int x[maxn], y[maxn], t[maxn];
int dp[maxn], big[maxn];
int main() {
  ios::sync_with_stdio(false);
  fast_input.tie(0);
  fast_input >> r >> n;
  for (long long i = (1); i <= (n); ++i) {
    fast_input >> t[i] >> x[i] >> y[i];
  }
  x[0] = 1, y[0] = 1, t[0] = 0;
  for (long long i = (1); i <= (n); ++i) {
    if (abs(x[i] - x[0]) + abs(y[i] - y[0]) > t[i]) dp[i] = -1e7;
    for (long long j = (i - 1); j >= (0); --j) {
      if (abs(x[i] - x[j]) + abs(y[i] - y[j]) <= t[i] - t[j])
        dp[i] = max(dp[i], dp[j] + 1);
      if (i > j + 2 * r) {
        dp[i] = max(dp[i], big[j] + 1);
        break;
      }
    }
    big[i] = max(dp[i], big[i - 1]);
  }
  int ans = 0;
  for (long long i = (1); i <= (n); ++i) ans = max(ans, dp[i]);
  fast_output << ans << '\n';
  return 0;
}
