#include<bits/stdc++.h>
using namespace std;
using P = pair<int, int>;
const long long LM = 1LL << 60;


vector<vector<P>> edge;

long long dfs(int p, int par, int to) {
    if (p == to) return 0;
    for (auto& e : edge[p]) {
        if (e.second == par) continue;
        long long d = dfs(e.second, p, to) + e.first;
        if (d < LM) return d;
    }
    return LM;
}

vector<long long> dp;

long long dfs(int p, int par, long long l, long long ds) {
    dp[p] += min(l, ds);
    for (auto& e : edge[p]) {
        if (e.second == par) continue;
        dp[p] = min(dp[p], dfs(e.second, p, l + e.first, ds));
    }
    return dp[p];
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    int n, q, c;
    cin >> n >> q >> c;
    edge = vector<vector<P>>(n);
    for (int i = 0; i < n - 1; ++i) {
        int u, v, l;
        cin >> u >> v >> l;
        --u;
        --v;
        edge[u].emplace_back(l, v);
        edge[v].emplace_back(l, u);
    }
    dp = vector<long long>(n, LM);
    int prev;
    cin >> prev;
    --prev;
    dp[prev] = 0;
    for (int i = 1; i < q; ++i) {
        int x;
        cin >> x;
        --x;
        long long d = dfs(prev, -1, x);
        dfs(x, -1, c, d);
        prev = x;
    }
    long long ans = LM;
    for (int i = 0; i < n; ++i) {
        ans = min(ans, dp[i]);
    }
    cout << ans << '\n';
    return 0;
}