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#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include <iostream>
#include <cmath>
#include <algorithm>
#include <fstream>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <string>
#include <cstring>
#include <unordered_set>
#include <unordered_map>
#include <random>
#include <chrono>
#include <ctime>
#include <complex>
#include <bitset>

using namespace std;

#define int long long
#define ld long double
#define nl "\n"
#define pb push_back
#define xx first
#define yy second
#define cinn(a) for (int i = 0; i < (int) a.size(); i++) cin >> a[i];
#define coutt(a) for (int i = 0; i < (int) a.size(); i++) cout << a[i] << (i == a.size() - 1 ? nl : " ");
#define sortt(a) sort(a.begin(), a.end());
#define rev(a) reverse(a.begin(), a.end());
#define hi(a) (--a.end())
#define lo(a) a.begin()
#define ll(a) int a; cin >> a;
#define vi(a, n) vector<int> a(n); cinn(a);
#define forn(i, n) for (int i = 0; i < n; i++)
#define nfor(i, n) for (int i = n; i >= 0; i--)
#define foreach(i, st) for (auto & i : st)

const int inf = 1e15 + 7;
const int N = 2e5 + 69;
const int M = 998244353;

vector<pair<int, int>> g[N];
int lca[N][20];
int lcaW[N][20];
int depth[N];

void dfs(int now, int last, int lastW, int d) {
    lca[now][0] = last;
    lcaW[now][0] = lastW;
    depth[now] = d;

    for (auto p : g[now]) {
        if (p.xx == last) continue;
        dfs(p.xx, now, p.yy, d + 1);
    }
}

int lcaweight(int a, int b) {
    if (depth[a] < depth[b]) swap(a, b);
    int dist = 0;
    for (int i = 19; i >= 0; i--) {
        if (depth[lca[a][i]] < depth[b]) continue;
        dist = max(dist, lcaW[a][i]);
        a = lca[a][i];
    }

    if (a == b) {
        return dist;
    }

    for (int i = 19; i >= 0; i--) {
        if (lca[a][i] == lca[b][i]) continue;
        dist = max(dist, max(lcaW[a][i], lcaW[b][i]));
        a = lca[a][i];
        b = lca[b][i];
    }

    dist = max(dist, max(lcaW[a][0], lcaW[b][0]));
    return dist;
}

void solve() {
    ll(n); ll(m);
    forn(i, n - 1) {
        ll(u); ll(v); ll(c);
        u--;v--;
        g[v].pb({ u, c });
        g[u].pb({ v, c });
    }

    vi(path, m);

    dfs(0, -1, 0, 0);

    for (int i = 1; i < 20; i++) {
        for (int j = 0; j < n; j++) {
            lcaW[j][i] = max(lcaW[j][i - 1], lcaW[lca[j][i - 1]][i - 1]);
            lca[j][i] = lca[lca[j][i - 1]][i - 1];
        }
    }

    forn(i, m) path[i]--;
    int res = 0;
    for (int i = 1; i < m; i++) {
        res += lcaweight(path[i], path[i - 1]);
    }
    cout << res << nl;
}

signed main()
{
    //freopen("magic.in", "r", stdin);
    //freopen("magic.out", "w", stdout);
#ifdef _DEBUG
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    int start = chrono::high_resolution_clock::now().time_since_epoch().count();
#endif
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cout << fixed;
    cout.precision(10);

    int tests = 1;
    //cin >> tests;
    while (tests--) solve();

#ifdef _DEBUG
    cout << nl << "TIME ms: ";
    cout << (chrono::high_resolution_clock::now().time_since_epoch().count() - start) / 1e6 << nl;
#endif
    return 0;
}