#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    unsigned int c;
    cin >> n >> c;
    vector <vector <pair <int, unsigned int>>> adj(n);
    vector <unsigned int> all_S;
    for (int i = 0; i < n - 1; ++i) {
        int a, b;
        unsigned int s;
        cin >> a >> b >> s;
        --a;
        --b;
        adj[a].emplace_back(b, s);
        adj[b].emplace_back(a, s);
        all_S.push_back(s);
    }
    sort(all_S.begin(), all_S.end());
    all_S.erase(unique(all_S.begin(), all_S.end()), all_S.end());
    reverse(all_S.begin(), all_S.end());
    constexpr unsigned int inf = numeric_limits <unsigned int>::max();
    vector <vector <unsigned int>> v_take(n);
    auto Dfs = [&](auto self, int root, int skip) {
        unsigned int best_n = c * adj[root].size();
        unsigned int max_adj = 0;
        unsigned int upwards = 0;
        for (auto e : adj[root]) {
            max_adj = max(max_adj, e.second);
            if (e.first == skip) upwards = e.second;
        }
        int count = all_S.size();
        while (count > 0 && all_S[count - 1] < max_adj) --count;
        v_take[root].resize(count);
        auto& best_t = v_take[root];
        for (int i = 0; i < count; ++i) {
            if (upwards > 0) best_t[i] = all_S[i] - upwards;
        }
        if (root == -1) return best_n;
        for (auto e : adj[root]) {
            if (e.first == skip) continue;
            auto child_ntake = self(self, e.first, root);
            const auto& child_take = v_take[e.first];
            unsigned int best_child = child_ntake;
            for (auto x : child_take) best_child = min(best_child, x);
            best_n += best_child;
            for (int i = 0; i < count; ++i) {
                unsigned int cur = child_ntake + all_S[i] - e.second;
                if (i < child_take.size()) cur = min(cur, child_take[i]);
                best_t[i] += cur;
            }
        }
        return best_n;
    };
    unsigned int ans = Dfs(Dfs, 0, -1);
    for (unsigned int x : v_take[0]) ans = min(ans, x);
    cout << ans << "\n";
    return 0;
}