#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll,ll>
#define pii pair<int,int>
#define fs first
#define sc second
#define tlll tuple<ll,ll,ll>
#define tiii tuple<int,int,int>
const int inf = 1e9+10;
const int mxn = 1e5+10;
vector<pii> paths[mxn];
vector<pii> dist[mxn];
priority_queue<tiii,vector<tiii>,greater<tiii>> pq;
ll N,M,K;
int sp[mxn];
vector<pair<int,pii>> v;
void DIJKSTRA(){
for(int i = 1;i<=K;i++){
int now = sp[i];
dist[now].push_back(make_pair(0,now));
sort(dist[now].begin(),dist[now].end());
pq.push(make_tuple(0,now,now));
}
while(!pq.empty()){
int d = get<0>(pq.top()),now = get<1>(pq.top()),f = get<2>(pq.top());
pq.pop();
bool flag = false;
for(auto &i:dist[now]){
if(i == make_pair(d,f))flag = true;
}
if(!flag)continue;
for(auto nxt:paths[now]){
if(dist[nxt.fs].size()<5||dist[nxt.fs].back().fs>=d+nxt.sc){
bool can = true;
int idx = -1;
for(int i = 0;i<dist[nxt.fs].size();i++){
if(dist[nxt.fs][i].sc == f){
if(dist[nxt.fs][i].fs<=d+nxt.sc)can = false;
else idx = i;
}
}
if(!can)continue;
if(idx == -1){
dist[nxt.fs].push_back({d+nxt.sc,f});
}
else{
dist[nxt.fs][idx].fs = d+nxt.sc;
}
sort(dist[nxt.fs].begin(),dist[nxt.fs].end());
pq.push(make_tuple(d+nxt.sc,nxt.fs,f));
while(dist[nxt.fs].size()>5)dist[nxt.fs].pop_back();
}
}
}
return;
}
int main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>N>>M>>K;
for(int i = 1;i<=M;i++){
int a,b,c;
cin>>a>>b>>c;
paths[a].push_back(make_pair(b,c));
paths[b].push_back(make_pair(a,c));
}
for(int i = 1;i<=K;i++)cin>>sp[i];
DIJKSTRA();
/*
for(int i = 1;i<=K;i++){
cout<<sp[i]<<":";for(auto &j:dist[sp[i]])cout<<j.fs<<','<<j.sc<<' ';cout<<endl;
}
*/
for(int i = 1;i<=K;i++){
for(auto &j:dist[sp[i]]){
if(j.sc == sp[i])continue;
v.push_back(make_pair(j.fs,make_pair(sp[i],j.sc)));
}
}
sort(v.begin(),v.end());
for(auto &i:v){
if(min(i.sc.fs,i.sc.sc) != 1){
cout<<i.fs+1;
return 0;
}
}
}
