using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Numerics;
namespace Tasks
{
public class E
{
public static void Main()
{
using var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
Console.SetOut(sw);
Solve();
Console.Out.Flush();
}
public static void Solve()
{
var (N, M, K) = Scanner.Scan<int, int, int>();
var G = new List<(int, int)>[N].Select(x => new List<(int, int)>()).ToArray();
const long inf = (long)1e18;
var Edges = new (int U, int V, long C)[M];
for (var i = 0; i < M; i++)
{
var (a, b, c) = Scanner.Scan<int, int, int>();
a--; b--;
G[a].Add((b, c));
G[b].Add((a, c));
Edges[i] = (a, b, c);
}
var E = Scanner.ScanEnumerable<int>().Select(x => x - 1).ToArray();
var set = new HashSet<int> { 0 };
var costs = new long[N];
Array.Fill(costs, inf);
costs[0] = 0;
for (var i = 0; i < K; i++)
{
var (a, b, c) = Edges[E[i]];
if (set.Contains(a))
{
costs[b] = Math.Min(costs[b], costs[a] + c);
set.Add(b);
}
}
var answer = costs[N - 1];
if (answer == inf) answer = -1;
Console.WriteLine(answer);
}
public static class Scanner
{
public static string ScanLine() => Console.ReadLine()?.Trim() ?? string.Empty;
public static string[] Scan() => ScanLine().Split(' ');
public static T Scan<T>() where T : IConvertible => Convert<T>(Scan()[0]);
public static (T1, T2) Scan<T1, T2>() where T1 : IConvertible where T2 : IConvertible
{
var line = Scan();
return (Convert<T1>(line[0]), Convert<T2>(line[1]));
}
public static (T1, T2, T3) Scan<T1, T2, T3>() where T1 : IConvertible where T2 : IConvertible where T3 : IConvertible
{
var line = Scan();
return (Convert<T1>(line[0]), Convert<T2>(line[1]), Convert<T3>(line[2]));
}
public static (T1, T2, T3, T4) Scan<T1, T2, T3, T4>() where T1 : IConvertible where T2 : IConvertible where T3 : IConvertible where T4 : IConvertible
{
var line = Scan();
return (Convert<T1>(line[0]), Convert<T2>(line[1]), Convert<T3>(line[2]), Convert<T4>(line[3]));
}
public static (T1, T2, T3, T4, T5) Scan<T1, T2, T3, T4, T5>() where T1 : IConvertible where T2 : IConvertible where T3 : IConvertible where T4 : IConvertible where T5 : IConvertible
{
var line = Scan();
return (Convert<T1>(line[0]), Convert<T2>(line[1]), Convert<T3>(line[2]), Convert<T4>(line[3]), Convert<T5>(line[4]));
}
public static (T1, T2, T3, T4, T5, T6) Scan<T1, T2, T3, T4, T5, T6>() where T1 : IConvertible where T2 : IConvertible where T3 : IConvertible where T4 : IConvertible where T5 : IConvertible where T6 : IConvertible
{
var line = Scan();
return (Convert<T1>(line[0]), Convert<T2>(line[1]), Convert<T3>(line[2]), Convert<T4>(line[3]), Convert<T5>(line[4]), Convert<T6>(line[5]));
}
public static IEnumerable<T> ScanEnumerable<T>() where T : IConvertible => Scan().Select(Convert<T>);
private static T Convert<T>(string value) where T : IConvertible => (T)System.Convert.ChangeType(value, typeof(T));
}
}
}