#include <bits/stdc++.h>
using namespace std;
template <class T>
T sqr(T x) {
  return x * x;
}
template <class T>
T gcd(T a, T b) {
  return (b != 0 ? gcd<T>(b, a % b) : a);
}
template <class T>
T lcm(T a, T b) {
  return (a / gcd<T>(a, b) * b);
}
template <class T>
inline T bigmod(T p, T e, T M) {
  if (e == 0) return 1;
  if (e % 2 == 0) {
    long long int t = bigmod(p, e / 2, M);
    return (T)((t * t) % M);
  }
  return (T)((long long int)bigmod(p, e - 1, M) * (long long int)p) % M;
}
template <class T>
inline T bigexp(T p, T e) {
  if (e == 0) return 1;
  if (e % 2 == 0) {
    long long int t = bigexp(p, e / 2);
    return (T)((t * t));
  }
  return (T)((long long int)bigexp(p, e - 1) * (long long int)p);
}
template <class T>
inline T modinverse(T a, T M) {
  return bigmod(a, M - 2, M);
}
int dx4[] = {1, 0, -1, 0};
int dy4[] = {0, 1, 0, -1};
int dx8[] = {1, 1, 0, -1, -1, -1, 0, 1};
int dy8[] = {0, 1, 1, 1, 0, -1, -1, -1};
int nx8[] = {1, 1, -1, -1, 2, 2, -2, -2};
int ny8[] = {2, -2, 2, -2, 1, -1, 1, -1};
int month[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
struct T {
  int u, v, w;
  bool operator<(const T& p) const { return w < p.w; }
} edges[300005];
struct TT {
  int val, last, pv, pl;
} dp[300005];
int n, m, u, v, w, in[300005];
int main() {
  scanf("%d %d", &n, &m);
  for (__typeof(m) i = (1); i <= (m); i++) {
    scanf("%d %d %d", &u, &v, &w);
    in[v]++;
    edges[i].u = u;
    edges[i].v = v;
    edges[i].w = w;
  }
  sort(edges + 1, edges + m + 1);
  for (__typeof(m) i = (1); i <= (m); i++) {
    if (dp[edges[i].u].last < edges[i].w) {
      if (dp[edges[i].v].val < dp[edges[i].u].val + 1) {
        dp[edges[i].v].pv = dp[edges[i].v].val;
        dp[edges[i].v].pl = dp[edges[i].v].last;
        dp[edges[i].v].val = dp[edges[i].u].val + 1;
        dp[edges[i].v].last = edges[i].w;
      }
    } else {
      if (dp[edges[i].v].val < dp[edges[i].u].pv + 1) {
        dp[edges[i].v].pv = dp[edges[i].v].val;
        dp[edges[i].v].pl = dp[edges[i].v].last;
        dp[edges[i].v].val = dp[edges[i].u].pv + 1;
        dp[edges[i].v].last = edges[i].w;
      }
    }
  }
  int mx = 0;
  for (__typeof(n) i = (1); i <= (n); i++) mx = max(mx, dp[i].val);
  cout << mx;
  return 0;
}
