#include <bits/stdc++.h>

using namespace std;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, c;
    cin >> n >> c;
    vector<vector<pair<int, int>>> g(n);
    vector<int> ws;
    for (int i = 0; i < n - 1; i++) {
        int x, y, w;
        cin >> x >> y >> w;
        --x; --y;
        g[x].emplace_back(y, w);
        g[y].emplace_back(x, w);
        ws.push_back(w);
    }
    ranges::sort(ws);
    ws.resize(unique(ws.begin(), ws.end()) - ws.begin());
    const int W = ws.size();
    for (int i = 0; i < n; i++) {
        for (auto& [_, w] : g[i]) {
            w = ranges::lower_bound(ws, w) - ws.begin();
        }
    }
    vector<int> pe_cost(n, -1);
    const int inf = 2e9 + 5;
    vector<vector<int>> dp(n, vector<int>(W));
    function<void(int, int)> Dfs = [&](int v, int p) {
        long long pay_cost = 0;
        for (auto [u, w] : g[v]) {
            if (u == p) {
                continue;
            }
            pe_cost[u] = w;
            Dfs(u, v);
            pay_cost += *ranges::min_element(dp[u]) + c;
            for (int j = 0; j < W; j++) {
                if (dp[v][j] == inf || dp[u][j] == inf) {
                    dp[v][j] = inf;
                } else {
                    dp[v][j] += dp[u][j];
                }
            }
        }
        if (p != -1) {
            pay_cost += c;
        }
        // cerr << "pay cost: " << v << ' ' << pay_cost << endl;
        long long pw = (p == -1 ? 0 : pe_cost[v]);
        for (int j = 0; j < W; j++) {
            if (j < pw) {
                dp[v][j] = inf;
            } else {
                long long pay = ws[j] - ws[pw];
                if (dp[v][j] < inf) {
                    dp[v][j] += pay;
                }
                dp[v][j] = min((long long) dp[v][j], pay_cost + pay);
            }
        }
    };
    Dfs(0, -1);
    // for (int i = 0; i < n; i++) {
    //     for (int j = 0; j < W; j++) {
    //         cerr << dp[i][j] << " \n"[j == W - 1];
    //     }
    // }
    int ans = inf;
    for (int j = 0; j < W; j++) {
        ans = min(ans, dp[0][j] - (ws[j] - ws[0]));
    }
    cout << ans << '\n';
    return 0;
}