#include<bits/stdc++.h>
#define fi first
#define se second
using namespace std;
const int N = 2e5+5, W = 1e6+5, inf = 1e9;
int n, k, sz[N];
int hmin[W], ans;
bool del[N];
vector<pair<int,int>> adj[N];
int Size(int x, int t)
{
sz[x] = 1;
for (auto [y, _] : adj[x])
{
if (y == t || del[y]) continue;
sz[x] += Size(y, x);
}
return sz[x];
}
int Centroid(int x, int size, int t = -1)
{
for (auto [y, _] : adj[x])
{
if (y == t || del[y]) continue;
if (2 * sz[y] > size)
return Centroid(y, size, x);
}
return x;
}
queue<int> q;
stack<pair<int, int>> path;
void dfs(int x, int t, int we = 0, int d = 0)
{
if (hmin[k - we] != inf)
ans = min(ans, hmin[k - we] + d);
for (auto [y, w] : adj[x])
{
if (del[y] || y == t) continue;
if (we + w <= k && d + 1 <= ans)
dfs(y, x, we + w, d + 1);
if (t == -1)
{
while (!path.empty())
{
auto [dist, h] = path.top();
path.pop();
hmin[dist] = min(hmin[dist], h);
}
}
}
if (t != -1)
{
q.push(we);
path.emplace(we, d);
}
else
{
while (!q.empty())
{
int dist = q.front();
q.pop();
hmin[dist] = inf;
}
}
}
void Decompose(int x)
{
x = Centroid(x, Size(x, -1));
del[x] = true;
dfs(x, -1);
for (auto e : adj[x])
{
int y = e.fi;
if(!del[y]) Decompose(y);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
n = N, k = K;
for (int i = 0; i < n-1; i++)
{
int u = H[i][0] + 1, v = H[i][1] + 1, w = L[i];
adj[u].emplace_back(v, w);
adj[v].emplace_back(u, w);
}
ans = inf;
for(int i = 1; i <= k; i++){
hmin[i] = inf;
}
Decompose(1);
return (ans == inf ? -1 : ans);
}
