#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pl = pair<ll,ll>;
using pii = pair<int,int>;
using tpl = tuple<int,int,int>;
#define all(a) a.begin(), a.end()
#define filter(a) a.erase(unique(all(a)), a.end())
const int mn = 1e5 + 5;
const int maxStage = 4;
int spec[mn], dist[maxStage][mn], optSource[maxStage][mn], n, m, k;
vector<pii> adj[mn], path[mn];
vector<int> visSource[mn];
priority_queue<tpl> pq;
struct IT {
vector<int> tr;
IT (int sz) : tr(4 * sz, INT_MAX) {}
void update (int pos, int val, int k, int l, int r) {
for (; l < r;) {
int mid = (l + r) >> 1;
if (pos <= mid) k <<= 1, r = mid;
else k <<= 1, k |= 1, l = mid + 1;
}
tr[k] = min(tr[k], val);
for (k >>= 1; k >= 1; k >>= 1)
tr[k] = min(tr[k << 1], tr[k << 1 | 1]);
}
int query (int a, int b, int k, int l, int r) {
if (b < l || r < a) return INT_MAX;
if (a <= l && r <= b) return tr[k];
int mid = (l + r) >> 1;
return min(query(a, b, k << 1, l, mid), query(a, b, k << 1 | 1, mid + 1, r));
}
};
struct ITRange {
vector<int> lazy;
ITRange (int sz) : lazy(4 * sz, INT_MAX) {}
void update (int a, int b, int val, int k, int l, int r) {
if (b < l || r < a) return;
if (a <= l && r <= b) return lazy[k] = min(lazy[k], val), void();
int mid = (l + r) >> 1;
update(a, b, val, k << 1, l, mid);
update(a, b, val, k << 1 | 1, mid + 1, r);
}
int query (int pos, int k, int l, int r) {
int ans = lazy[k];
for (; l < r;) {
int mid = (l + r) >> 1;
if (pos <= mid) k <<= 1, r = mid;
else k <<= 1, k |= 1, l = mid + 1;
ans = min(ans, lazy[k]);
}
return ans;
}
};
void addPath (int u, int v, int w) {
if (w == INT_MAX) return;
path[max(u, v)].emplace_back(min(u, v), w);
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
/// read input & preprocess
cin >> n >> m >> k;
while (m--) {
int a, b, c; cin >> a >> b >> c;
adj[a].emplace_back(b, c);
adj[b].emplace_back(a, c);
}
for (int i = 1; i <= n; i++)
for (int j = 0; j < maxStage; j++) dist[j][i] = INT_MAX;
for (int i = 1; i <= k; i++) {
cin >> spec[i];
pq.emplace(0, spec[i], spec[i]);
}
/// multi-core dijkstra
int threshold = 0;
while (pq.size() && threshold < 5 * n) {
int dst, u, source; tie(dst, u, source) = pq.top(); pq.pop();
if (visSource[u].size() >= maxStage || find(all(visSource[u]), source) != visSource[u].end()) continue;
int stage = visSource[u].size();
dst = -dst, dist[stage][u] = dst, optSource[stage][u] = source;
visSource[u].push_back(source), threshold++;
for (pii item : adj[u]) {
int v, w; tie(v, w) = item;
if (dst + w < dist[maxStage - 1][v])
if (find(all(visSource[v]), source) == visSource[v].end()) pq.emplace(-(dst + w), v, source);
}
}
/// solve
for (int i = 1; i <= k; i++) {
int u = spec[i];
for (int j = 1; j < maxStage; j++)
addPath(u, optSource[j][u], dist[j][u]);
}
int ans = INT_MAX;
IT treeLeft(n), treeRight(n);
ITRange treeRange(n);
for (int i = 1; i <= n; i++) {
for (pii item : path[i]) {
int j, w; tie(j, w) = item;
int cur = min({treeRight.query(1, j - 1, 1, 1, n),
treeLeft.query(j + 1, n, 1, 1, n),
treeRange.query(j, 1, 1, n)});
if (cur != INT_MAX) ans = min(ans, cur + w);
}
for (pii item : path[i]) {
int j, w; tie(j, w) = item;
treeLeft.update(j, w, 1, 1, n);
treeRight.update(i, w, 1, 1, n);
if (j + 1 <= i - 1)
treeRange.update(j + 1, i - 1, w, 1, 1, n);
}
}
cout << (ans == INT_MAX ? -1 : ans);
return 0;
}
