#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <stack>
#include <cassert>
#include <map>
#include <numeric>
#include <cstring>
#include <set>
#include <ctime>
#include <array>
#include <queue>
#include <cmath>
#include <iomanip>
#include <iterator>
#include <bitset>
#include <unordered_map>
#include <complex>
#include <unordered_set>
#include <chrono>
#include <random>
#include <functional>
#include <random>
#include <complex>

using namespace std;
using namespace std::chrono;

class InputReader {
public:
    InputReader() {
        input_file = stdin;
        cursor = 0;
        fread(buffer, SIZE, 1, input_file);
    }

    InputReader(const char *file_name) {
        input_file = fopen(file_name, "r");
        cursor = 0;
        fread(buffer, SIZE, 1, input_file);
    }

    template<typename T>
    inline InputReader &operator>>(T &n) {
        while ((buffer[cursor] < '0' || buffer[cursor] > '9') && buffer[cursor] != '-') {
            advance();
        }
        int sign = 1;
        if (buffer[cursor] == '-') {
            sign = -1;
            advance();
        }
        n = 0;
        while ('0' <= buffer[cursor] && buffer[cursor] <= '9') {
            n = n * 10 + buffer[cursor] - '0';
            advance();
        }
        n *= sign;
        return *this;
    }

    inline InputReader &operator>>(char *s) {
        while (!isalpha(buffer[cursor])) {
            advance();
        }
        int len = 0;
        while (isalpha(buffer[cursor])) {
            s[len] = buffer[cursor];
            len++;
            advance();
        }
        s[len] = 0;
        return *this;
    }

private:
    FILE *input_file;
    static const int SIZE = 1 << 17;
    int cursor;
    char buffer[SIZE];

    inline void advance() {
        ++cursor;
        if (cursor == SIZE) {
            cursor = 0;
            fread(buffer, SIZE, 1, input_file);
        }
    }
};

const int MAXN = 20000;
const long long INF = 1000000000000000000LL;

vector<pair<int, int>> g[1 + MAXN];
vector<int> v;
int c;
int weight[1 + MAXN];
long long dp0[1 + MAXN];
vector<long long> dp1[1 + MAXN];

void getWeights(int node, int father) {
    weight[node] = 1;
    int biggest = 0, where = -1;
    for (int i = 0; i < g[node].size(); i++) {
        int son = g[node][i].first;
        if (son != father) {
            getWeights(son, node);
            weight[node] += weight[son];
            if (weight[son] > biggest) {
                biggest = weight[son];
                where = i;
            }
        }
    }
    if (where != -1 && where != 0) {
        swap(g[node][0], g[node][where]);
    }
}

void DFS(int node, int father) {
    int k = v.size();
    for (auto [son, s] : g[node]) {
        if (son != father) {
            DFS(son, node);
            dp1[node].resize(k);
            long long best = INF;
            for (int i = 0; i < k; i++) {
                if (s > v[i]) {
                    dp1[node][i] = INF;
                } else {
                    dp1[node][i] += v[i] - s + min(dp0[son] + c, dp1[son][i]);
                    best = min(best, v[i] - s + dp1[son][i]);
                }
            }
            dp0[node] += c + min(dp0[son] + c, best);
            dp1[son] = {};
        }
    }
    dp1[node].resize(k);
}

int main() {
 //   ifstream cin("input.txt");
//    ofstream cout("output.txt");
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    srand(time(0));

    int n;
    cin >> n >> c;
    for (int i = 1; i < n; i++) {
        int a, b, s;
        cin >> a >> b >> s;
        g[a].push_back({b, s});
        g[b].push_back({a, s});
        v.push_back(s);
    }
    sort(v.begin(), v.end());
    v.resize(unique(v.begin(), v.end()) - v.begin());
    getWeights(1, 0);
    DFS(1, 0);
    long long ans = dp0[1];
    for (int i = 0; i < v.size(); i++) {
        ans = min(ans, dp1[1][i]);
    }
    cout << ans << "\n";

//    auto stopTime = high_resolution_clock::now();
//    auto duration = duration_cast<milliseconds>(stopTime - startTime);
//    cout << "Ellapsed time: " << duration.count() << "\n";
    return 0;
}