#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
vector<vector<int>> g[300005], a;
int n, k, c[300005], dd[300005], res = 999999999;
int dfs(int x, int p) {
c[x] = 1;
for (auto w : g[x]) {
if (w[0] != p && dd[w[0]] == 0) {
c[x] += dfs(w[0], x);
}
}
return c[x];
}
void dfs2(int x, int p, int v, int num, int d) {
for (auto w : g[x]) {
if (w[0] != p && dd[w[0]] == 0) {
dfs2(w[0], x, v + w[1], num + 1, d);
}
}
a.push_back({v, num, d});
}
int centroid(int x, int sz, int p) {
for (auto w : g[x]) {
if (w[0] != p && dd[w[0]] == 0 && c[w[0]] * 2 > sz) {
return centroid(w[0], sz, x);
}
}
return x;
}
void trya(int x, int p) {
int c = centroid(x, dfs(x, -1), -1), d = 0;
a.clear();
for (auto w : g[c]) {
if (dd[w[0]] == 0) {
dfs2(w[0], c, w[1], 1, d);
}
a.push_back({0, 0, d});
d++;
}
sort(a.begin(), a.end());
int l = 0, r = a.size() - 1;
while (l <= r) {
if (a[l][0] + a[r][0] > k) {
r--;
}
else if (a[l][0] + a[r][0] == k) {
if (a[l][2] == a[r][2]) {
if (a[r][0] != a[r - 1][0]) {
l++;
continue;
}
r--;
continue;
}
else {
res = min(res, a[l][1] + a[r][1]);
r--;
}
}
else if (a[l][0] + a[r][0] < k) {
l++;
}
}
dd[c] = 1;
for (auto w : g[c]) {
if (dd[w[0]] == 0) {
trya(w[0], c);
}
}
}
int best_path(int N, int K, int H[][2], int L[]) {
n = N;
k = K;
for (int i = 0; i < n - 1; i++) {
g[H[i][0]].push_back({H[i][1], L[i]});
g[H[i][1]].push_back({H[i][0], L[i]});
}
trya(0, -1);
if (res == 999999999) return -1;
return res;
}
