// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops", "omit-frame-pointer", "inline")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,abm,mmx,avx,avx2,fma,tune=native")
// #pragma GCC option("arch=native", "no-zero-upper") // Enable AVX

/// UH Top
#include <bits/stdc++.h>
#define db(x) cerr << #x << ':' << (x) << '\n';
#define all(v) (v).begin(), (v).end()
#define allr(v) (v).rbegin(), (v).rend()
// #define int ll
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
// typedef __int128_t int128;
typedef pair<ll, ll> pii;
typedef pair<ld, ll> pdi;
typedef pair<ld, ld> pdd;
typedef pair<ld, pdd> pdp;
typedef pair<string, ll> psi;
typedef pair<ll, string> pls;
typedef pair<string, string> pss;
typedef pair<ll, pii> pip;
typedef pair<pii, pii> ppp;
typedef complex<ld> point;
typedef vector<point> polygon;
typedef vector<ll> vi;
typedef pair<point, int> ppi;
#define prec(n)        \
    cout.precision(n); \
    cout << fixed
const ll mod = (1e9 + 7);
const ld eps = (1e-9);
const ll oo = (ll)(1e18 + 5);
#define pi acos(-1)
#define MAXN (ll)(2e4 + 5)

int cont, c;
vector<int> vs;
int trans[MAXN * 5];
int dp[MAXN][MAXN];
vector<pii> g[MAXN];
ll ans;

void dfs(int u, int p, int w)
{
    vector<int> sons;
    for (auto e : g[u])
        if (e.first != p)
        {
            dfs(e.first, u, e.second);
            sons.push_back(e.first);
        }

    if (sons.empty() && u)
    {
        int ini = trans[w];
        for (int i = 0; i < cont; i++)
        {
            if (i < ini)
                dp[u][i] = 2e9;
            else
                dp[u][i] = vs[i] - vs[ini];
        }
    }
    else if(u)
    {
        int ini = trans[w];
        ll mi = 0;
        for (auto v : sons)
        {
            int add = 2e9;
            for (int i = 0; i < cont; i++)
                add = min(add, dp[v][i]);
            mi += add;
        }
        for (int i = 0; i < cont; i++)
        {
            if (i < ini)
                dp[u][i] = 2e9;
            else
            {
                ll x1 = 0;
                for (auto v : sons)
                    x1 += dp[v][i];

                dp[u][i] = min(((ll)2e9), x1 + vs[i] - vs[ini]);
                if(dp[u][i]>mi + vs[i] - vs[ini] + 1ll * (sons.size() + 1) * c)
                    dp[u][i]=mi + vs[i] - vs[ini] + 1ll * (sons.size() + 1) * c;
            }
        }
    }

    if(!u)
    {
        ll mi = 0;
        for (auto v : sons)
        {
            int add = 2e9;
            for (int i = 0; i < cont; i++)
                add = min(add, dp[v][i]);
            mi += add;
        }
        ans=mi+1ll*sons.size()*c;
        for (int i = 0; i < cont; i++)
        {
            ll x1 = 0;
            for (auto v : sons)
                x1 += dp[v][i];

            ans=min(ans,x1);
        }
    }
}

int32_t main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int n;
    cin >> n >> c;
    set<int> ww;
    for (int i = 0; i < n - 1; i++)
    {
        int u, v, w;
        cin >> u >> v >> w;
        u--, v--;
        g[u].push_back(pii(v, w));
        g[v].push_back(pii(u, w));
        ww.insert(w);
    }

    for (auto x : ww)
    {
        trans[x] = cont;
        vs.push_back(x);
        cont++;
    }

    dfs(0, -1, -1);

    cout << ans << '\n';

    return 0;
}