#include<iostream>
#include<vector>
#include<string>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<random>
using namespace std;
random_device __RD; mt19937 Rand(__RD());
#define For(i,j,k) for(int i=j;i<=k;i++)
#define Rep(i,j,k) for(int i=j;i>=k;i--)
//#define ls(c) c<<1
//#define rs(c) c<<1|1
#define int long long
#define lowbit(x) ((x)&(-x))
template<typename type>
inline void read(type &x){
    x=0;bool flag(0);char ch=getchar();
    while(!isdigit(ch)) flag^=ch=='-',ch=getchar();
    while(isdigit(ch)) x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    flag?x=-x:0;
}
template<typename type>
inline void write(type x){
    x<0?x=-x,putchar('-'):0;
    static short Stack[50],top(0);
    do Stack[++top]=x%10,x/=10;while(x);
    while(top) putchar(Stack[top--]|48);
}
inline char read(char &ch){return ch=getchar();}
inline char write(const char &ch){return putchar(ch);}
template<typename type,typename ...T>
inline void read(type &x,T&...y){read(x),read(y...);}
template<typename type,typename ...T>
inline void write(type x,T...y){write(x),putchar(' '),write(y...),sizeof...(y)^1?0:putchar('\n');}
const int N=1e5+5,Mod=1e9+7;
int n,m,a,b,k,ans;
int rt[N],tot,ls[N<<2],rs[N<<2],t[N<<2];
void push_up(int c){
	t[c]=max(t[ls[c]],t[rs[c]]);
}
void update(int &c,int l,int r,int x,int k){
	if(l>r||k<0) return;
	if(!c) c=++tot;
	if(l==r){
		t[c]=max(t[c],k);
		return;
	}
	int mid=(l+r)>>1;
	if(x<=mid) update(ls[c],l,mid,x,k);
	else update(rs[c],mid+1,r,x,k);
	push_up(c);return;
}
int query(int &c,int l,int r,int ql,int qr){
	if(ql>qr||l>r||c==0) return 0;
	if(ql<=l&&qr>=r) return t[c];
	int mid=(l+r)>>1,res=0;
	if(l<=mid) res=query(ls[c],l,mid,ql,qr);
	if(r>mid) res=max(res,query(rs[c],mid+1,r,ql,qr));
	return res;
}
signed main(){
//	ios::sync_with_stdio(false);
//	cin.tie(0);cout.tie(0);
	read(n);read(m);
	For(i,1,m){
		read(a);read(b);read(k);
		int Q=query(rt[a],0,N,0,k-1)+1;
//		cout<<"Q="<<Q<<endl;
		update(rt[b],0,N,k,Q);
	}
	For(i,1,n) ans=max(ans,t[rt[i]]);
	write(ans);
	return 0;
}
/*
10 100000
887 867 48640
935 970 58161
812 918 46665
331 493 46450
77 10 67235
108 748 26995
733 819 48677
191 982 46257
909 229 55735
282 5 52994
939 765 85635
74 466 50728
890 246 63410
938 437 46151
606 562 71629
577 735 5536
992 623 34758
61 937 14508
600 274 5651
172 295 46932
607 209 78278
927 635 16102
674 506 75360
62 311 22553
200 591 37988
84 189 7402
138 301 26621
57 334 37254
562 308 86313
94 547 20942
659 109 93133
204 647 12663
149 196 10922
269 332 12288
*/