acpc2016day2D.cpp

struct edge {
    int to, cost;
    edge(){}
    edge(int _to, int _cost) : to(_to), cost(_cost) {}
};
using Graph = vector<vector<edge>>;
vector<int> dijkstra(const Graph& G, int s, int g) {
    int n = G.size();
    priority_queue<Pii, vector<Pii>, greater<Pii>> pq;   // cost, vertex
    vi d(n, inf);
    d[s] = 0;
    pq.push(make_pair(0, s));

    while (!pq.empty()) {
        auto p = pq.top(); pq.pop();
        int v = p.second;
        if (v == g) break;
        if (d[v] < p.first) continue;
        for (const auto& e : G[v]) {
            if (d[v] <= e.cost && d[e.to] > e.cost) {
                d[e.to] = e.cost;
                pq.push(make_pair(d[e.to], e.to));
            }
        }
    }
    return d;
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int N, M;
    cin >> N >> M;
    Graph G(N);
    rep(i, M) {
        int a, b, c;
        cin >> a >> b >> c;
        a--, b--;
        G[a].emplace_back(b, c);
    }

    auto d = dijkstra(G, 0, -1);

    int ans = -1;
    rep(i, N) {
        for (auto e : G[i]) {
            if (e.to == N - 1 && d[i] <= e.cost) {
                ans = max(ans, e.cost);
            }
        }
    }

    cout << ans << endl;
}