#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#ifndef _AAAAAAAAA
#include "race.h"
#endif
using namespace std;
using namespace __gnu_pbds;
#pragma region dalykai
using p32 = pair<int, int>;
using p32u = pair<uint32_t, uint32_t>;
using p64 = pair<int64_t, int64_t>;
using p64u = pair<uint64_t, uint64_t>;
using vi16 = vector<int16_t>;
using vi16u = vector<uint16_t>;
using vi32 = vector<int>;
using vi32u = vector<uint32_t>;
using vi64 = vector<int64_t>;
using vi64u = vector<uint64_t>;
using vp32 = vector<p32>;
using vp32u = vector<p32u>;
using vp64 = vector<p64>;
using vp64u = vector<p64u>;
using vvi32 = vector<vi32>;
using vvi32u = vector<vi32u>;
using vvi64 = vector<vi64>;
using vvi64u = vector<vi64u>;
using vvp32 = vector<vp32>;
using vvp32u = vector<vp32u>;
using vvp64 = vector<vp64>;
using vvp64u = vector<vp64u>;
#pragma endregion
using state_t = bitset<(int)2e5>;
using map_t = map<int, int>;
void merge_maps(map_t &path, map_t &new_path)
{
if (path.size() < new_path.size())
{
new_path.swap(path);
}
for (auto &[sum, len] : new_path)
{
auto it = path.find(sum);
if (it == path.end())
{
path.emplace(sum, len);
}
else
{
it->second = min(it->second, len);
}
}
}
void find_size(int v, int p,
vi32 &size, vvp32 &adj, state_t &deleted)
{
if (deleted[v])
{
size[v] = 0;
return;
}
size[v] = 1;
for (auto &[next, len] : adj[v])
{
if (next == p || deleted[v])
{
continue;
}
find_size(next, v, size, adj, deleted);
size[v] += size[next];
}
}
void find_centroid(int v, int p, int needed,
int ¢roid,
vi32 &size, vvp32 &adj, state_t &deleted)
{
if (deleted[v])
{
return;
}
bool ok = true;
for (auto &[next, len] : adj[v])
{
if (size[next] <= needed || next == p || deleted[next])
{
continue;
}
find_centroid(next, v, needed, centroid, size, adj, deleted);
ok = false;
break;
}
if (centroid == -1 && ok)
{
centroid = v;
}
}
int update_length(int sum, int length, map_t &map)
{
auto it = map.find(sum);
if (it == map.end())
{
map[sum] = length;
return length;
}
it->second = min(it->second, length);
return length;
}
void find_paths(int v, int p, int sum, int length, int K,
int &shortest,
map_t &path, map_t &new_path, vvp32 &adj, state_t &deleted)
{
if (sum > K || deleted[v])
{
return;
}
if (sum == K)
{
shortest = min(shortest, length);
return;
}
int cur_length = update_length(sum, length, new_path);
auto it = path.find(K - sum);
if (it != path.end())
{
shortest = min(shortest, it->second + cur_length);
}
for (auto &[next, len] : adj[v])
{
if (next == p || deleted[next])
{
continue;
}
find_paths(next, v, sum + len, length + 1, K,
shortest,
path, new_path, adj, deleted);
}
}
void eval_centroid(int v, int K,
int &shortest,
vi32 &size, vvp32 &adj, state_t &deleted)
{
find_size(v, -1, size, adj, deleted);
if (size[v] < 2)
{
return;
}
int centroid = -1;
find_centroid(v, -1, size[v] / 2, centroid, size, adj, deleted);
deleted[centroid] = true;
map_t path;
for (auto &[next, len] : adj[centroid])
{
if (deleted[next])
{
continue;
}
map_t new_path;
find_paths(next, -1, len, 1, K, shortest, path, new_path, adj, deleted);
merge_maps(path, new_path);
}
for (auto &[next, len] : adj[centroid])
{
if (deleted[next])
{
continue;
}
eval_centroid(next, K, shortest, size, adj, deleted);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
vvp32 adj(N);
for (int i = 0; i < N - 1; i++)
{
adj[H[i][0]].emplace_back(H[i][1], L[i]);
adj[H[i][1]].emplace_back(H[i][0], L[i]);
}
int shortest = N + 1;
vi32 size(N);
state_t deleted;
eval_centroid(0, K, shortest, size, adj, deleted);
return shortest == N + 1 ? -1 : shortest;
}
#ifdef _AAAAAAAAA
#define MAX_N 500000
static int N, K;
static int H[MAX_N][2];
static int L[MAX_N];
void read_input()
{
int i;
scanf("%d %d", &N, &K);
for (i = 0; i < N - 1; i++)
scanf("%d %d %d", &H[i][0], &H[i][1], &L[i]);
}
int main()
{
freopen("race.in", "r", stdin);
int ans;
read_input();
ans = best_path(N, K, H, L);
printf("%d\n", ans);
return 0;
}
#endif
