#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
const int N = 20010;
int n, C, fc[N], fmn[N];
int f[N][N];
vector<pii> g[N];
vector<int> L;
inline void Dp(int x, int fa) {
    int sm = 0, bnd = 0;
    for (auto [y, z]: g[x]) if (y != fa) {
        fc[y] = lower_bound(L.begin(), L.end(), z) - L.begin() + 1;
        Dp(y, x);
        sm += fmn[y];
        bnd = max(bnd, fc[y]);
        for (int j = bnd; j <= L.size(); ++j) f[x][j] += f[y][j];
    }
    sm += C * (x == 1 ? g[x].size() : g[x].size() - 1);
    fmn[x] = 2e9;
    for (int j = fc[x]; j <= L.size(); ++j) {
        int delta = L[j - 1];
        if (x != 1) delta -= L[fc[x] - 1];
        if (x == 1) delta = 0;
        if (j < bnd) f[x][j] = 2e9;
        f[x][j] = min(sm, f[x][j]) + delta;
        fmn[x] = min(fmn[x], f[x][j]);
    }
    
}
signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> C;
    for (int i = 1, x, y, z; i < n; ++i) {
        cin >> x >> y >> z;
        L.push_back(z);
        g[x].push_back(pii(y, z));
        g[y].push_back(pii(x, z));
    }
    sort(L.begin(), L.end());
    L.erase(unique(L.begin(), L.end()), L.end());
    Dp(1, 0);
    cout << fmn[1] << endl;
    return 0;
}