#include <iostream>
#include <vector>
#include <queue>
#include <limits>

using namespace std;

struct Edge {
    int to;
    long long cost;
};

const long long INF = numeric_limits<long long>::max();

int main() {
    int N, M;
    cin >> N >> M;

    vector<long long> W(N + 1);
    for (int i = 1; i <= N; ++i) {
        cin >> W[i];
    }

    vector<vector<Edge>> graph(N + 1);

    for (int i = 0; i < M; ++i) {
        int U, V;
        long long T;
        cin >> U >> V >> T;
        graph[U].push_back({V, T});
        graph[V].push_back({U, T});
    }

    // ダイクストラ法の準備
    priority_queue<pair<long long, int>, vector<pair<long long, int>>, greater<pair<long long, int>>> pq;
    vector<long long> dist(N + 1, INF);

    dist[1] = 0;
    pq.push({0, 1});

    while (!pq.empty()) {
        auto [current_dist, u] = pq.top();
        pq.pop();

        if (current_dist > dist[u]) continue;

        // 通常の航路での更新
        for (const auto& edge : graph[u]) {
            int v = edge.to;
            long long cost = edge.cost;

            if (dist[u] + cost < dist[v]) {
                dist[v] = dist[u] + cost;
                pq.push({dist[v], v});
            }
        }

        // ワープによる更新
        for (int v = 1; v <= N; ++v) {
            if (u != v) {
                long long warp_cost = W[u] * W[v];
                if (dist[u] + warp_cost < dist[v]) {
                    dist[v] = dist[u] + warp_cost;
                    pq.push({dist[v], v});
                }
            }
        }
    }

    cout << dist[N] << endl;

    return 0;
}