#include <bits/stdc++.h>
using namespace std;
void fastIO() {
  std::ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
template <typename T, typename U>
inline void mnze(T &x, U y) {
  if (y < x) x = y;
}
template <typename T, typename U>
inline void mxze(T &x, U y) {
  if (x < y) x = y;
}
void _scan(int &x) { scanf("%d", &x); }
void _scan(long long &x) { scanf("%lld", &x); }
void _scan(double &x) { scanf("%lf", &x); }
void _scan(char &x) { scanf(" %c", &x); }
void _scan(char *x) { scanf("%s", x); }
template <typename T>
void _scan(vector<T> &v) {
  for (int i = 0; i < (int)v.size(); i++) _scan(v[i]);
}
void scan() {}
template <typename T, typename... U>
void scan(T &head, U &...tail) {
  _scan(head);
  scan(tail...);
}
template <typename T>
void _dbg(const char *sdbg, T h) {
  cerr << sdbg << "=" << h << "\n";
}
template <typename T, typename... U>
void _dbg(const char *sdbg, T h, U... t) {
  while (*sdbg != ',') cerr << *sdbg++;
  cerr << "=" << h << ",";
  _dbg(sdbg + 1, t...);
}
long long MOD = 1e9 + 7;
inline long long Msum(long long x) { return x; }
template <typename... Rest>
inline long long Msum(long long x, Rest... rest) {
  return (x + Msum(rest...)) % MOD;
}
inline long long Mprod(long long x) { return x; }
template <typename... Rest>
inline long long Mprod(long long x, Rest... rest) {
  return x * Mprod(rest...) % MOD;
}
inline long long Mnorm(long long x) { return (x % MOD + MOD) % MOD; }
const int MAXN = 1e5 + 5;
int n, m;
vector<tuple<int, int, int>> e;
map<int, int> w2len[MAXN];
void minsert(int v, int w, int len) {
  if (w2len[v].count(w) == 0) {
    w2len[v][w] = len;
  } else {
    int prevlen = w2len[v][w];
    if (len > prevlen) w2len[v][w] = len;
  }
  while (true) {
    auto it = w2len[v].find(w);
    if (it == w2len[v].begin()) break;
    auto it2 = it;
    it2--;
    if (it2->second <= it->second) {
      w2len[v].erase(it2);
    } else
      break;
  }
  auto it = w2len[v].find(w);
  auto it2 = it;
  it2++;
  if (it2 != w2len[v].end()) {
    if (it->second <= it2->second) {
      w2len[v].erase(it);
    }
  }
}
int main() {
  scan(n, m);
  for (int i = 0; i < m; i++) {
    int v, u, w;
    scan(v, u, w);
    v--;
    u--;
    e.push_back({v, u, w});
  }
  int ans = 0;
  for (int i = m - 1; i > -1; i--) {
    auto [v, u, w] = e[i];
    auto it = w2len[u].upper_bound(w);
    int len;
    if (it == w2len[u].end())
      len = 1;
    else
      len = 1 + it->second;
    mxze(ans, len);
    minsert(v, w, len);
  }
  printf("%d\n", ans);
}
