1. #include <cstdio>
    2. #include <algorithm>
    3. #include <cstring>
    4. #include <cstdlib>
    5. #include <vector>
    6. #include <iostream>
    7. using namespace std;
    8. inline int gi(){
    9.     char tmp=getchar();int ans=0;
    10.     while(!isdigit(tmp)) tmp=getchar();
    11.     while(isdigit(tmp)){
    12.         ans = ans * 10 + tmp - '0';
    13.         tmp=getchar();
    14.     }
    15.     return ans;
    16. }
    17. const int N = 1e6;
    18. struct Node{
    19.     int u,v;
    20. };
    21. vector<Node> V[N];
    22. int F[3][N];
    23. #define pb push_back
    24. signed main()
    25. {
    26. #ifdef TSUKIAKIOI
    27.     freopen("data.in","r",stdin);
    28. #endif
    29.     int n,m;    
    30.     n=gi(),m=gi();
    31.     int maxx = 0;
    32.     for(int i=1;i<=m;++i){
    33.         int u,v,w;
    34.         u=gi(),v=gi(),w=gi();
    35.         V[w].pb(Node{u,v});
    36.         maxx = max(maxx,w);
    37.     }
    38.     int ans = 0;
    39.     int tot = 0;
    40.     for(int i=1;i<=maxx+1;++i){
    41.         int len = V[i].size();
    42.         if(!len) continue;
    43.         ++tot;
    44.         for(int j=0;j<len;++j){
    45.             int u = V[i][j].u;int v = V[i][j].v;
    46.             F[1][0] = 1;
    47.         }
    48.         for(int j=0;j<len;++j){
    49.             int u = V[i][j].u;int v = V[i][j].v;
    50.             F[1][v] = max(F[1][v],F[0][u]+1);
    51.             ans = max(ans,F[1][v]);
    52.         }
    53.         for(int j=0;j<len;++j){
    54.             int u = V[i][j].u;int v = V[i][j].v;
    55.             F[0][v] = F[1][v];
    56.         }
    57.     }    
    58.     printf("%d\n",ans);
    59.     return 0;
    60. }