#include<iostream>
#include<cassert>
#include<set>
using namespace std;

#define rep(i,n) for(int i=0;i<(n);i++)

using i64=long long;
int main(){

  int n, m, k; cin>> n>> m>> k;
  assert(1<=n and n<=100000);
  assert(0<=m and m<=100000);
  assert(0<=k and k<=m);
  assert(n-1<=m);
  assert((i64)m<=(i64)n*(n-1)/2);

  set<pair<int, int>> edgeset;
  rep(_, m){
    int a, b; i64 c;
    cin>> a>> b>> c;
    assert(1<=a and a<=n);
    assert(1<=b and b<=n);
    assert(1<=c and c<=1000000000);
    assert(a<b);
    auto r=edgeset.insert({a, b}).second;
    assert(r==true);
  }
  assert((int)edgeset.size()==m);

  set<int> idset;
  rep(_, k){
    int i; cin>> i;
    assert(1<=i and i<=m);
    auto r=idset.insert(i).second;
    assert(r==true);
  }
  assert((int)idset.size()==k);

  cout<< -1<< endl;
  return 0;
}