#include <bits/stdc++.h>
#include "race.h"
using namespace std;
const int NMAX = 2e5;
const int INF = 1e9;
const int KMAX = 1e6;
int totalSize;
vector<pair<int, int>> edges[NMAX];
int sz[NMAX];
int centroidParent[NMAX];
bool isIn[NMAX];
int minimumDist[KMAX];
vector<long long> used;
int kk;
int ans;
int dfsCalcSize(int node, int parent) {
sz[node] = 1;
for(auto child : edges[node]) {
if(child.first != parent && isIn[child.first]) {
sz[node] += dfsCalcSize(child.first, node);
}
}
return sz[node];
}
int dfsDetCentroid(int node, int parent) {
for(auto child : edges[node]) {
if(child.first != parent && sz[child.first] > totalSize / 2 && isIn[child.first]) {
return dfsDetCentroid(child.first, node);
}
}
return node;
}
void computeDist(int node, int parent, int depth, long long sum, int flag) {
if(sum > kk)
return;
used.push_back(sum);
if(flag == true) {
ans = min(ans, minimumDist[kk - sum] + depth);
} else {
minimumDist[sum] = min(minimumDist[sum], depth);
}
for(auto child : edges[node]) {
if(isIn[child.first] && child.first != parent) {
computeDist(child.first, node, depth + 1, sum + child.second, flag);
}
}
}
void decompose(int root, int parent) {
totalSize = dfsCalcSize(root, root);
int centroid = dfsDetCentroid(root, root);
isIn[centroid] = false;
minimumDist[0] = 0;
for(auto child : edges[centroid]) {
if(isIn[child.first]) {
computeDist(child.first, centroid, 1, child.second, true);
computeDist(child.first, centroid, 1, child.second, false);
}
}
for(auto x : used) {
minimumDist[x] = INF;
}
used.clear();
centroidParent[centroid] = parent;
for(auto child : edges[centroid]) {
if(isIn[child.first])
decompose(child.first, centroid);
}
}
int best_path(int n, int k, int h[][2], int len[]) {
for(int i = 0; i < n - 1; i++) {
edges[h[i][0]].push_back({h[i][1], len[i]});
edges[h[i][1]].push_back({h[i][0], len[i]});
}
kk = k;
for(int i = 0; i <= k; i++)
minimumDist[i] = INF;
for(int i = 0; i < n; i++)
isIn[i] = true;
ans = INF;
decompose(0, -1);
if(ans == INF)
ans = -1;
return ans;
}
/*int h[NMAX][2];
int len[NMAX];
int main() {
int n, k;
cin >> n >> k;
for(int i = 0; i < n - 1; i++)
cin >> h[i][0] >> h[i][1];
for(int i = 0; i < n - 1; i++)
cin >> len[i];
cout << best_path(n, k, h, len);
return 0;
}*/
