#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> P;
typedef vector<ll> VI;
typedef vector<VI> VVI;
#define REP(i,n) for(int i=0;i<n;i++)
#define ALL(v) v.begin(),v.end()
constexpr ll MOD=998244353;
constexpr ll INF=1e18;

struct edge { 
	ll to, cost; 
};
struct qu {
	ll d; int v;
	bool operator<(const qu &another) const {return d > another.d;};
};
int n, q, c;
vector<edge> G[4000];
vector<ll> d(4000, INF);
vector<ll> bd(4000, INF);

void dijkstra(int s, bool f){
	priority_queue<qu> que;
	if(f){
		REP(i,n){
			que.push(qu{bd[i]+c,i});
			d[i]=bd[i]+c;
		}
		que.push(qu{bd[n],s});
		d[s]=bd[n];
	}
	else{
		REP(i,n){
			d[i]=INF;
		}
		que.push(qu{0,s});
		d[s]=0;
	}
	while(!que.empty()){
		qu p=que.top();
		que.pop();
		int v=p.v;
		if(d[v]<p.d) continue;
		REP(i,G[v].size()){
			edge e=G[v][i];
			if(d[e.to]>d[v]+e.cost){
				d[e.to]=d[v]+e.cost;
				que.push(qu{d[e.to],e.to});
			}
		}
	}
}

int main(){
	cin >> n >> q >> c;
	int u, v, l;
	REP(i,n-1){
		cin >> u >> v >> l;
		u--, v--;
		G[u].push_back({v,l});
		G[v].push_back({u,l});
	}
	int x, pre;
	cin >> pre; pre--;
	vector<ll> bdt(n,0);
	bd[n]=0;
	REP(i,q-1){
		cin >> x; x--;
		dijkstra(pre,1);
		REP(i,n) bdt[i]=d[i];
		ll bdn=d[x];
		dijkstra(x,0);
		REP(i,n) bd[i]=min(bd[i]+d[pre],bdt[i]+d[i]);
		bd[n]=bdn;
		pre=x;
	}
	cout << bd[n] << endl;
	return 0;
}