#include <bits/stdc++.h>
#define sz(v) (int)v.size()
#define all(v) v.begin(), v.end()

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

const ll inf = 0x3f3f3f3f3f3f3f3f;

void solve() {
    int n, c;
    cin >> n >> c;
    vector<vector<pii>> e(n);
    vi s(n);
    for (int i = 0; i < n - 1; i++) {
        int u, v, w;
        cin >> u >> v >> w;
        u--;
        v--;
        s[i] = w;
        e[u].emplace_back(v, w);
        e[v].emplace_back(u, w);
    }
    sort(all(s));
    s.erase(unique(all(s)), s.end());
    vector dp(n, vector<ll>(sz(s), inf));

    auto dfs = [&](auto&& dfs, int u, int f = -1, int fw = -1) -> void {
        ll sum = 0;
        for (auto [v, w] : e[u])
            if (v != f) {
                dfs(dfs, v, u, w);
                sum += *min_element(all(dp[v]));
            }
        int st = (int)(lower_bound(all(s), fw) - s.begin());
        for (int i = st; i < sz(s); i++) {
            if (fw == -1) dp[u][i] = min(dp[u][i], sum + (ll)c * sz(e[u]));
            else dp[u][i] = min(dp[u][i], sum + s[i] - fw + (ll)c * sz(e[u]));
        }
        for (int i = st; i < sz(s); i++) {
            ll tmp = 0;
            bool ok = true;
            for (auto [v, w] : e[u])
                if (v != f) {
                    if (dp[v][i] == inf) {
                        ok = false;
                        break;
                    }
                    tmp += dp[v][i];
                }
            if (ok) {
                if (fw == -1) dp[u][i] = min(dp[u][i], tmp);
                else dp[u][i] = min(dp[u][i], tmp + s[i] - fw);
            }
        }
    };

    dfs(dfs, 0);
    cout << *min_element(all(dp[0])) << '\n';
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(10);
    int T = 1;
    // cin >> T;
    while (T--) solve();
    return 0;
}