#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = (n)-1; i >= 0; --i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

constexpr ll inf = 1e18;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, q, c;
    cin >> n >> q >> c;
    vector<vector<P>> to(n);
    rep(i, n - 1) {
        int u, v, l;
        cin >> u >> v >> l;
        --u, --v;
        to[u].emplace_back(v, l);
        to[v].emplace_back(u, l);
    }
    VVL dist(n, VL(n, inf));
    rep(s, n) {
        VI vs{s};
        dist[s][s] = 0;
        while(!vs.empty()) {
            int u = vs.back(); vs.pop_back();
            for(auto [v, l]: to[u]) {
                if (dist[s][v] != inf) continue;
                dist[s][v] = dist[s][u] + l;
                vs.push_back(v);
            }
        }
    }
    VI x(q);
    rep(i, q) cin >> x[i], x[i]--;
    VL dp(n, inf);
    dp[x[0]] = 0;
    rep(i, q - 1) {
        VL ndp = dp;
        rep(u, n) ndp[u] += dist[x[i]][x[i+1]];
        VL d(n, inf);
        priority_queue<pair<ll,int>,vector<pair<ll,int>>,greater<pair<ll,int>>> q;
        auto push = [&](int v, ll c) {
            if (c < d[v]) {
                d[v] = c;
                q.emplace(c, v);
            }
        };
        push(x[i], dp[x[i]]);
        rep(u, n) push(u, dp[u] + c);
        while(!q.empty()) {
            auto [cost, u] = q.top(); q.pop();
            if (cost != d[u]) continue;
            for(auto [v, l]: to[u]) {
                push(v, cost + l);
            }
        }
        rep(u, n) chmin(ndp[u], d[u] + dist[u][x[i+1]]);
        dp = move(ndp);
    }
    ll ans = dp[x[q-1]];
    cout << ans << endl;
}