#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
const int N = 300005;
const double PI = 4 * atan(1);
const long long MAX = 9223372036854775807;
int dx[] = {1, -1, 0, 0, 1, -1, 1, -1};
int dy[] = {0, 0, 1, -1, 1, 1, -1, -1};
long long gcd(long long a, long long b) { return (b == 0 ? a : gcd(b, a % b)); }
long long lcm(long long a, long long b) { return a * (b / gcd(a, b)); }
bool issquare(long long w) { return trunc(sqrt(w)) * trunc(sqrt(w)) == w; }
bool isprime(long long u) {
  for (long long i = 2; i <= (int)sqrt(u); i++) {
    if (u % i == 0) return 0;
  }
  return 1;
}
long long mod(long long to_mod, long long MOD) {
  to_mod %= MOD;
  while (to_mod < 0) to_mod += MOD;
  return to_mod % MOD;
}
long long moduloMultiplication(long long a, long long b, long long mod) {
  long long res = 0;
  a %= mod;
  while (b) {
    if (b & 1) res = (res + a) % mod;
    a = (2 * a) % mod;
    b >>= 1;
  }
  return res;
}
long long power(long long x, long long y) {
  long long res = 1;
  x = x;
  while (y > 0) {
    if (y & 1) res = (res * x);
    y = y >> 1;
    x = (x * x);
  }
  return res;
}
long long n, m, x, y, res, t, k, ans = 0, q, z, w, l, a, b;
vector<pair<long long, pair<long long, long long> > > v;
long long dp[N];
vector<long long> vv;
long long curr[N];
int main() {
  ios::sync_with_stdio(0);
  memset(dp, 0, sizeof(dp));
  memset(curr, 0, sizeof(curr));
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    cin >> x >> y >> z;
    x--;
    y--;
    v.push_back(make_pair(z, make_pair(x, y)));
  }
  sort(v.begin(), v.end());
  ans = 1;
  for (int i = 0; i < m;) {
    long long j = i;
    vv.clear();
    while (j < m && v[j].first == v[i].first) {
      curr[v[j].second.second] =
          max(curr[v[j].second.second], 1 + dp[v[j].second.first]);
      vv.push_back(v[j].second.second);
      j++;
    }
    i = j;
    for (auto t : vv) {
      dp[t] = max(dp[t], curr[t]);
    }
  }
  for (int i = 0; i < n; i++) {
    ans = max(ans, dp[i]);
  }
  cout << ans;
  return 0;
}
