#include <iostream>
#include <vector>
#include <cassert>
#include <queue>

using namespace std;
using ll = long long;
using ld = long double;

const int INF = (1 << 30) - 10;
const ll LINF = 1LL << 60;

inline void output_YesNo(bool x) { cout << (x ? "Yes" : "No") << endl; }

template<typename T>
inline void chmax(T &lhs, const T &rhs) { lhs = max(lhs, rhs); }

template<typename T>
inline void chmin(T &lhs, const T &rhs) { lhs = min(lhs, rhs); }

// #include <iomanip>
//
// void init_output() { cout << fixed << setprecision(15); }

struct edge {
    int to;
    ll cost;
};

struct status {
    ll cost;
    int v;

    bool operator<(const status &rhs) const { return cost < rhs.cost; };

    bool operator>(const status &rhs) const { return cost > rhs.cost; };
};

vector<ll> dijkstra(int s, vector<vector<edge>> &graph) {
    priority_queue<status, vector<status>, greater<>> que;
    vector<ll> dis(graph.size(), LINF);
    dis[s] = 0;
    que.push({0, s});

    while (!que.empty()) {
        status now = que.top();
        que.pop();

        if (dis[now.v] < now.cost)continue;

        for (auto next: graph[now.v]) {
            if (dis[next.to] > now.cost + next.cost) {
                dis[next.to] = now.cost + next.cost;
                que.push({dis[next.to], next.to});
            }
        }
    }

    return dis;
}

int main() {
    int n, m, k;
    cin >> n >> m >> k;
    vector<ll> cost(m);
    for (auto &x: cost)cin >> x;

    vector<vector<edge>> graph(n * (k + 1));
    for (int i = 0; i < m; i++) {
        int from, to;
        cin >> from >> to, from--, to--;
        for (int j = 0; j <= k; j++) {
            int u = from + n * j;
            int v = to + n * j;
            graph[u].push_back({v, cost[i]});
            graph[v].push_back({u, cost[i]});

            if (j >= 1) {
                graph[u].push_back({v - n, 0});
                graph[v].push_back({u - n, 0});
            }
        }
    }

    vector<ll> dis = dijkstra(n * k, graph);
    cout << (dis[n - 1] >= LINF ? -1 : dis[n - 1]) << endl;
    return 0;
}