/*
* Author: illuz 
* Blog: http://blog.csdn.net/hcbbt
* File: E.cpp
* Create Date: 2014-08-16 09:43:59
* Descripton: 
*/

#include 
#include 
#include 
#include 
using namespace std;
#define repf(i,a,b) for(int i=(a);i<=(b);i++)

const int N = 3e5 + 10;

struct Edge {
	int x;
	int y;
	int w;
	bool operator <(const Edge& e) const {
	return w < e.w;
	}
} e[N];

int n, m;
int edge[N], node[N];	// edges and nodes' dp

int main() {
	while (~scanf("%d%d", &n, &m)) {
	memset(edge, 0, sizeof(edge));
	memset(node, 0, sizeof(node));

	repf (i, 1, m) {
	scanf("%d%d%d", &e[i].x, &e[i].y, &e[i].w);
	}

	sort(e + 1, e + m + 1);

	repf (i, 1, m) {
	int j = i;
	while (j <= m && e[i].w == e[j].w) {	// update edges' dp
	int x = e[j].x;
	edge[j] = max(edge[j], node[x] + 1);
	j++;
	}

	j = i;
	while (j <= m && e[i].w == e[j].w) {	// update nodes' dp
	int y = e[j].y;
	node[y] = max(edge[j], node[y]);
	j++;
	}
	i = j - 1;
	}

	int ans = 0;
	repf (i, 1, m)
	ans = max(ans, edge[i]);

	printf("%d\n", ans);
	}
	return 0;
}