//  Shopping in JOI Kingdom.cpp
//  2013/01/06.

#if 1

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iostream>
#include <cctype>
#include <sstream>
#include <string>
#include <list>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <utility>
#include <numeric>
#include <algorithm>
#include <iterator>
#include <bitset>
#include <complex>
#include <fstream>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
template<class T> T RoundOff(T a){ return int(a+.5-(a<0)); }
template<class T, class C> void chmax(T& a, C b){ if(a < b) a = b; }
template<class T, class C> void chmin(T& a, C b){ if(b < a) a = b; }
template<class T, class C> pair<T, C> mp(T a, C b){ return make_pair(a, b); }

const int INF = 1<<30;

int N, M, K;
int D[3000];
int C[3000][3000];
int used[3000];

int dfs(int pnt)
{
	rep(next, N) if(D[next] > D[pnt] + C[pnt][next])
	{
		D[next] = D[pnt] + C[pnt][next];
		dfs(next);
	}
}

void dijkstra(int pnt)
{
	memset(used, 0, sizeof used);
	
	while(true)
	{
		int v = -1;
		
		rep(u, N) if(!used[u] && (v == -1 || D[u] < D[v])) v = u;
		
		if(v == -1) break;
		
		used[v] = true;
		
		rep(u, N) chmin(D[u], D[v] + C[v][u]);
	}
}

int calc(int a, int b, int l)
{
	return round(min(a, b) + (l + max(a, b) - min(a, b)) / 2.0);
}

int main()
{
	rep(i, 3000) rep(j, 3000) D[i] = C[i][j] = INF;
	
	cin >> N >> M >> K;

	rep(m, M)
	{
		int a, b, c;
		cin >> a >> b >> c;
		
		C[a-1][b-1] = C[b-1][a-1] = c;
	}
	
	int s;
	rep(k, K)
	{
		cin >> s;
		
		D[s-1] = 0;
	}
	
	dijkstra(0);

	int ans = 0;
	
	rep(a, N) REP(b, a+1, N) if(C[a][b] < INF) chmax(ans, calc(D[a], D[b], C[a][b]));
	
	cout << ans << endl;
}

#endif