#include <bits/stdc++.h>
#ifdef LOCAL
#include "debug.h"
#else
#define dbg(...) 42
#include "race.h"
#endif
int best_path(int n, int k, int H[][2], int L[]) {
std::vector<std::vector<std::pair<int, int>>> g(n);
for (int i = 0; i + 1 < n; ++i) {
g[H[i][0]].emplace_back(H[i][1], L[i]);
g[H[i][1]].emplace_back(H[i][0], L[i]);
}
std::vector<int> size(n);
std::vector<bool> died(n, false);
auto dfs_sz = [&](auto& f, int v, int p) -> int {
size[v] = 1;
for (auto [u, _] : g[v]) {
if (u != p && !died[u]) {
size[v] += f(f, u, v);
}
}
return size[v];
};
auto centroid = [&](auto& f, int v, int p, int desired) -> int {
for (auto [u, _] : g[v]) {
if (u != p && !died[u] && size[u] >= desired) {
return f(f, u, v, desired);
}
}
return v;
};
constexpr auto inf = std::numeric_limits<int>::max() / 2;
std::vector<int> min_cnt(k + 1, inf);
auto dfs_calc = [&](auto& f, int v, int p, int tot_w, int cnt, bool do_update, std::set<int>& touched) -> int {
auto loc = inf;
if (tot_w > k) {
return loc;
}
if (do_update) {
min_cnt[tot_w] = std::min(min_cnt[tot_w], cnt);
touched.emplace(tot_w);
} else {
loc = std::min(loc, cnt + min_cnt[k - tot_w]);
}
for (auto [u, w] : g[v]) {
if (u != p && !died[u]) {
loc = std::min(loc, f(f, u, v, tot_w + w, cnt + 1, do_update, touched));
}
}
return loc;
};
auto CD = [&](auto& f, int v, int p) -> int {
auto c = centroid(centroid, v, p, dfs_sz(dfs_sz, v, p) / 2);
died[c] = true;
auto loc = inf;
std::set<int> touched;
for (auto [u, w] : g[c]) {
if (!died[u]) {
loc = std::min(loc, dfs_calc(dfs_calc, u, c, w, 1, false, touched));
assert(dfs_calc(dfs_calc, u, c, w, 1, true, touched) == inf);
}
}
for (auto w : touched) {
min_cnt[w] = inf;
}
for (auto [u, _] : g[c]) {
if (!died[u]) {
loc = std::min(loc, f(f, u, c));
}
}
return loc;
};
min_cnt[0] = 0;
auto res = CD(CD, 0, -1);
return res == inf ? -1 : res;
}
#ifdef LOCAL
void solve() {
int n, k;
std::cin >> n >> k;
int H[n][2], L[n];
for (int i = 0; i + 1 < n; ++i) {
std::cin >> H[i][0] >> H[i][1] >> L[i];
}
std::cout << best_path(n, k, H, L) << '\n';
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
solve();
}
#endif
