#include<cstdio>

#include<algorithm>

#include<iostream>

using namespace std;

const int maxn = 1000000 + 4;

const int inf = 100000 + 4;

int  n, m;

int root[maxn],  maxv[maxn << 2],ch[maxn << 2][2], cnt;

inline void get_max(int &a,int b)

{

    if(b > a) a = b;

}

struct Segment_Tree

{

    #define lson ch[o][0]

    #define rson ch[o][1]

    inline void update(int l,int r,int delta,int val,int &o)

    {

        if(!o) o = ++cnt;

        if(l == r)

        {

            get_max(maxv[o], delta);

            return;

        }

        int mid = (l + r) >> 1;

        if(val <= mid)

            update(l, mid, delta, val, ch[o][0]);

        else

            update(mid + 1, r, delta, val, ch[o][1]);

        get_max(maxv[o], max(maxv[lson], maxv[rson]));

    }

    inline int query(int l,int r,int L,int R,int o)

    {

        if(!o) return 0;

        if(l > r || r < L || l > R  || L > R)  return 0;

        if(l >= L && r <= R)

            return maxv[o];

        int mid = (l + r) >> 1;

        return max(query(l, mid, L, R, lson), query(mid + 1, r, L, R, rson));

    }

}T;

int main()

{

    //freopen("input.in","r",stdin);

    scanf("%d%d",&n,&m);

    int ans = 0;

    for(int i = 1;i <= m; ++i)

    {

        int from, to, val;

        scanf("%d%d%d",&from, &to,&val);

        ++ val;

        int tmp = T.query(1, inf , 1, val - 1, root[from]);

        T.update(1, inf, tmp + 1, val, root[to]);

        get_max(ans, tmp + 1);

    }

    printf("%d",ans);

    return 0;

}