cf960F

#include<bits/stdc++.h>
#define forn(i, n) for (int i = 0 ; i < int(n) ; i++)
#define fore(i, s, t) for (int i = s ; i < (int)t ; i++)
#define fi first
#define se second
#define all(x) x.begin(),x.end()
#define pf2(x,y) printf("%d %d\n",x,y)
#define pf(x) printf("%d\n",x)
#define each(x) for(auto it:x)  cout<<it<<endl;
#define pi pair<int,int>
using namespace std;
typedef long long ll;
const int maxn=1e6+5;
const int maxm=2e5+5;
const int inf=1e9;
vector<map<int,int>> s;
int calc(int a,int w){
	auto it=s[a].lower_bound(w);
	if(it==s[a].begin()) return 1;
	it--;
	return (it->second)+1;
}
int main(){
	int n,m;
	cin>>n>>m;
	s.resize(n+1);
	int ans=0;
	for(int i=0;i<m;i++){
		int x,y,z;
		cin>>x>>y>>z;
		int val=calc(x,z);
		if(calc(y,z+1)>val) continue;
		s[y][z]=max(s[y][z],val);
		auto it=s[y].upper_bound(z); 
		while(!(it==s[y].end() || it->se>val))
			it=s[y].erase(it);
		ans=max(ans,val);
	}	
	cout<<ans<<endl;
}