#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define ed '\n'
#define pb push_back
#define ii pair<ll,ll>
#define fi first
#define se second
using namespace std;
const ll N = 2e5 + 10;
ii lazy[N];
vector<ii> g[N];
ll n, k, ans = 1e18;
map<ll, ll> f[N];
void Merge(ll u, ll v) {
if (f[u].size() < f[v].size()) {
swap(lazy[u], lazy[v]);
f[u].swap(f[v]);
}
for(pair<ll, ll> tmp: f[v]) {
ll num = tmp.fi + lazy[v].fi;
ll Min = tmp.se + lazy[v].se;
auto t = f[u].find(k - num - lazy[u].fi);
if (t != f[u].end()) {
if (t->se + Min + lazy[u].se < ans) {
ans = t->se + Min + lazy[u].se;
}
}
if (f[u][num - lazy[u].fi] == 0) f[u][num - lazy[u].fi] = Min - lazy[u].se;
else {
if (Min - lazy[u].se < f[u][num - lazy[u].fi]) {
f[u][num - lazy[u].fi] = Min - lazy[u].se;
}
}
}
}
void dfs(ll u, ll p, ll val) {
f[u][0] = 0;
for(ii &e: g[u]) if (e.fi != p) {
dfs(e.fi, u, e.se);
Merge(u, e.fi);
}
lazy[u].fi += val;
lazy[u].se ++;
}
ll best_path(int N, int K, int H[][2], int L[]) {
n = N, k = K;
for(ll i=0;i<n-1;i++)
{
g[H[i][0]].pb({H[i][1],L[i]});
g[H[i][1]].pb({H[i][0],L[i]});
}
dfs(0, -1, 0);
if (ans == 1e18) ans = -1;
return ans;
}
