#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#include<vector>
#include<algorithm>
using namespace std;
struct node
{
    int to,value;
};
vector<node> nxt[1005];      //向量+结构体 邻接表
int in_degree[1005];          //节点的入度
int finish[1005];            //节点的开始时间
int m, n;
void topo() {
    queue <int> q;
    
    for (int i = 0; i < n; i++)
        if (in_degree[i] == 0) {
            finish[i] = 1;
            q.push(i);
        }
            
    while (!q.empty()) {
        int now = q.front(); q.pop();
        for (int i = 0; i < nxt[now].size(); i++) {
            int to = nxt[now][i].to;
            int v = nxt[now][i].value;
            in_degree[to]--;
            finish[to] = max(finish[to], finish[now] + v);
            if (in_degree[to] == 0) q.push(to);
        }
    }
    int tp = 1;
    for (int i = 0; i < n; i++) {
        tp = max(tp, finish[i]);
    }
    printf("%d\n", tp);
}
int main() {
    while (cin >> n >> m) {
        fill(finish, finish + 1005, 0);
        fill(in_degree, in_degree + 1005, 0);
        for(int i = 0; i < n; i++)
            nxt[i].clear();
        for (int i = 0; i < m; i++) {
            int a, b, c;
            scanf("%d %d %d", &a, &b, &c);
            in_degree[b]++;
            node no;
            no.to = b;
            no.value = c;
            nxt[a].push_back(no);
        }
        topo();
    }

    return 0;
}