import java.awt.Point;
import java.util.*;
public class f {
	Scanner in=new Scanner(System.in);
	public static void main(String[] args) {
		new f().go();
	}
	private void go() {
		int n=in.nextInt(),m=in.nextInt(),p=in.nextInt();
		ArrayList<HashMap<Integer,Integer>> al=new ArrayList<HashMap<Integer,Integer>>();
		for(int i=0;i<n+1;i++)al.add(new HashMap<Integer,Integer>());
		HashSet<Integer> is=new HashSet<Integer>();
		for(int i=0;i<p;i++)is.add(in.nextInt());
		for(int i=0;i<m;i++){
			int x=in.nextInt(),y=in.nextInt(),l=in.nextInt();
			al.get(x).put(y, l);
			al.get(y).put(x, l);
		}
		ArrayList<Point> mst = MST2(al,is);
		int ans=0;
		for(Point ps:mst)ans+=al.get(ps.x).get(ps.y);
		if(p==n){//every city is insecure...must be fully connected
			for(int i=1;i<n;i++)for(int j=i+1;j<=n;j++){
				if(!al.get(i).containsKey(j)){
					System.out.println("impossible");
					System.exit(0);
				}
				ans+=al.get(i).get(j);
			}
		} else {//some node is in the MST....must take cheapest link
			for(int i:is){
				int min=Integer.MAX_VALUE;
				for(int j:al.get(i).keySet())if(!is.contains(j))min=Math.min(min, al.get(i).get(j));
				if(min==Integer.MAX_VALUE){//no link to MST.
					System.out.println("impossible");
					System.exit(0);
				}
				ans+=min;
			}
		}
		System.out.println(ans);
	}
	public ArrayList<Point> MST2(ArrayList<HashMap<Integer,Integer>> in,HashSet<Integer>is){
		ArrayList<Point> out=new ArrayList<Point>();
		HashSet<Integer> visited=new HashSet<Integer>(is);
		final ArrayList<HashMap<Integer,Integer>> al=new ArrayList<HashMap<Integer,Integer>>(in);
		PriorityQueue<Point> pq=new PriorityQueue<Point>(al.size(), new Comparator<Point>(){
			public int compare(Point o1, Point o2) {
				double d=al.get(o1.x).get(o1.y)-al.get(o2.x).get(o2.y);
				if(d!=0)return (int) Math.signum(d);
				if(o1.x!=o2.x)return o1.x-o2.x;
				return o1.y-o2.y;
			}
		});
		int first=1;
		while(visited.contains(first))first++;
		visited.add(0);
		visited.add(first);
		if(first>=al.size())return out;//all points are insecure...no MST
		for(int i:in.get(first).keySet())pq.offer(new Point(first,i));
		while(!pq.isEmpty()){
			Point t=pq.poll();
			if(visited.contains(t.y))continue;
			visited.add(t.y);
			out.add(t);
			for(int i:in.get(t.y).keySet())	if(!visited.contains(i))pq.offer((new Point(t.y,i)));
		}
		if(visited.size()!=al.size()){//graph is disconnected
			System.out.println("impossible");
			System.exit(0);
		}
		return out;
	}
}