#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>

using namespace std;

int main(){
    int n, m;
    while(cin >> n >> m) {
        vector<vector<pair<int, int>>> adj(n + 1);
        vector<int> degree(n + 1, 0);
        vector<pair<pair<int, int>, int>> edges;
        queue<int> q;
        vector<int> topo;
        vector<int> ve(n + 1, 0);
        for(int i = 0; i < m; i++) {
            int a, b, w;
            cin >> a >> b >> w;
            a--; b--;
            adj[a].push_back(make_pair(b, w));
            degree[b]++;
            edges.push_back(make_pair(make_pair(a, b), w));
        }
        for(int i = 0; i < n; i++) {
            if(degree[i] == 0) {
                q.push(i);
            }
        }
        while(!q.empty()) {
            int u = q.front();
            q.pop();
            topo.push_back(u);
            for(auto [v, w] : adj[u]) {
                degree[v]--;
                if(degree[v] == 0) {
                    q.push(v);
                }
            }
        }
        //topo为拓扑排序
        if(topo.size() != n) {
            cout << "unworkable project" << endl;
            continue;
        }
        //正向一次，求出最早开始时间
        for(int i = 0; i < topo.size(); i++) {
            int u = topo[i];
            for(auto [v, w] : adj[u]) {
                ve[v] = max(ve[v], ve[u] + w);
            }
        }
        int max_ve = 0;
        for(int i = 0; i < n; i++) {
            max_ve = max(max_ve, ve[i]);
        }
        //反向一次，求出最晚开始时间
        vector<int> vl(n + 1, max_ve);
        for(int i = topo.size() - 1; i >= 0; i--) {
            int u = topo[i];
            for(auto [v, w] : adj[u]) {
                vl[u] = min(vl[u], vl[v] - w);
            }
        }

        cout << max_ve << endl;

        //判断是否关键路径
        vector<pair<int, int>> is_critical;
        for(auto e : edges) {
            int a = e.first.first;
            int b = e.first.second;
            int w = e.second;
            if(ve[a] + w == vl[b]) {
                is_critical.push_back(make_pair(a, b));
            }
        }
        sort(is_critical.begin(), is_critical.end());
        for(auto [a, b] : is_critical) {
            a++; b++;
            cout << a << "->" << b << endl;
        }
    }

    return 0;
}