#include <bits/stdc++.h>
using namespace std;

template <typename T>
void chmin(T &a, T b) {
    if (b < a) {
        a = b;
    }
}

using graph = vector<vector<pair<int64_t, int64_t>>>;

void dfs(const graph &to, vector<int64_t> &dist, int v, int par) {
    for (auto [next, l] : to[v]) {
        if (next == par) continue;
        dist[next] = dist[v] + l;
        dfs(to, dist, next, v);
    }
}

int main() {
    constexpr int64_t inf = 1e18;
    int64_t n, q, c;
    cin >> n >> q >> c;
    graph to(n);
    for (int i = 0; i < n - 1; i++) {
        int64_t u, v, l;
        cin >> u >> v >> l;
        u--; v--;
        to[u].emplace_back(v, l);
        to[v].emplace_back(u, l);
    }
    vector<int> x(q);
    for (int i = 0; i < q; i++) {
        cin >> x[i];
        x[i]--;
    }
    vector dist(n, vector(n, int64_t()));
    for (int i = 0; i < n; i++) {
        dfs(to, dist[i], i, -1);
    }

    vector dp(q, vector(n, inf));
    dp.at(0).at(x.at(0)) = 0;
    for (int i = 1; i < q; i++) {
        int64_t mincost_prev = *min_element(dp[i - 1].begin(), dp[i - 1].end());
        vector<int64_t> with_teleport(n, inf);
        for (int j = 0; j < n; j++) {
            chmin(with_teleport[j], dp[i - 1][j] + c + dist[j][x[i]]);
        }
        for (int j = 0; j < n; j++) {
            chmin(dp[i][j], dp[i - 1][j] + dist[x[i - 1]][x[i]]);
            int64_t diff = dist[x[i - 1]][j] + dist[j][x[i]] - dist[x[i - 1]][x[i]];
            assert(diff % 2 == 0);
            chmin(dp[i][j], mincost_prev + dist[x[i - 1]][x[i]] + diff / 2);
            if (diff) continue;
            if (dist[x[i - 1]][x[i]] + dist[x[i]][j] != dist[x[i - 1]][j]) continue;
            chmin(dp[i][j], with_teleport[x[i]]);
        }
    }
    cout << dp[q - 1][x[q - 1]] << endl;
}