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#include <iostream>
#include <vector>
#include <queue>
#include <climits>
#include <unordered_set>

using namespace std;

typedef long long ll;

int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);

int P, C, K;
cin >> P >> C >> K;

vector<vector<pair<int, int>>> graph(P);
for (int i = 0; i < C; ++i) {
    int a, b, L;
    cin >> a >> b >> L;
    a--; b--; // Convert to 0-based index.
    graph[a].emplace_back(b, L);
    graph[b].emplace_back(a, L);
}

unordered_set<int> largeFarms;
if (K > 0) {
    for (int i = 0; i < K; ++i) {
        int farm;
        cin >> farm;
        farm--;
        largeFarms.insert(farm);
    }
}

vector<ll> minDist(P, LLONG_MAX);
priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> pq;

// Initialize the priority queue with all large farms as sources.
for (int farm : largeFarms) {
    minDist[farm] = 0;
    pq.emplace(0, farm);
}

// Multi-source Dijkstra's algorithm.
while (!pq.empty()) {
    auto [currentDist, u] = pq.top();
    pq.pop();

    if (currentDist > minDist[u]) continue;

    for (auto [v, weight] : graph[u]) {
        if (minDist[v] > currentDist + weight) {
            minDist[v] = currentDist + weight;
            pq.emplace(minDist[v], v);
        }
    }
}

// Find the minimum distance among non-large farms.
ll result = LLONG_MAX;
for (int i = 0; i < P; ++i) {
    if (largeFarms.find(i) == largeFarms.end() && minDist[i] < result) {
        result = minDist[i];
    }
}

if (result == LLONG_MAX) {
    cout << -1 << endl;
} else {
    cout << result << endl;
}

return 0;

}