//Copyright © 2022 Youngmin Park. All rights reserved.
//#pragma GCC optimize("O3")
//#pragma GCC target("avx2")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
using vpi = vector<pii>;
using pll = pair<ll, ll>;
using vl = vector<ll>;
using vpl = vector<pll>;
using ld = long double;
template <typename T, size_t SZ>
using ar = array<T, SZ>;
#define all(v) (v).begin(), (v).end()
#define pb push_back
#define sz(x) (int)(x).size()
#define fi first
#define se second
#define lb lower_bound
#define ub upper_bound
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define F0R(i, a) FOR(i, 0, a)
#define ROF(i, a, b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i, a) ROF(i, 0, a)
#define REP(a) F0R(_, a)
const int INF = 1e9;
const ll LINF = 1e18;
const int MOD = 1e9 + 7; //998244353;
const ld PI = acos((ld)-1.0);
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T>
using pqg = priority_queue<T, vector<T>, greater<T>>;
template <typename T>
bool ckmin(T &a, const T &b) { return b < a ? a = b, 1 : 0; }
template <typename T>
bool ckmax(T &a, const T &b) { return b > a ? a = b, 1 : 0; }
template <typename A, typename B>
ostream &operator<<(ostream &os, const pair<A, B> &p)
{
return os << '(' << p.first << ", " << p.second << ')';
}
template <typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type>
ostream &operator<<(ostream &os, const T_container &v)
{
os << '{';
string sep;
for (const T &x : v)
os << sep << x, sep = ", ";
return os << '}';
}
void dbg_out()
{
cerr << endl;
}
template <typename Head, typename... Tail>
void dbg_out(Head H, Tail... T)
{
cerr << ' ' << H;
dbg_out(T...);
}
#ifdef LOCAL
#define dbg(...) cerr << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...) 42
#endif
inline namespace RecursiveLambda{
template <typename Fun>
struct y_combinator_result{
Fun fun_;
template <typename T>
explicit y_combinator_result(T &&fun): fun_(forward<T>(fun)){}
template <typename...Args>
decltype(auto) operator()(Args &&...args){
return fun_(ref(*this), forward<Args>(args)...);
}
};
template <typename Fun>
decltype(auto) y_combinator(Fun &&fun){
return y_combinator_result<decay_t<Fun>>(forward<Fun>(fun));
}
};
void setIO(string s) // USACO
{
#ifndef LOCAL
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
#endif
}
const int MN = 1e6;
const int MX = 2e5;
vpi adj[MX];
vi v[MX];
pair<int, ll> up[20][MX];
int sub[MX], depth[MX];
int targ;
int ans = INF;
ll shift = 0;
map<ll, int> cnt;
int extra = 0;
void init(int u, int pu) {
sub[u] = 1;
for (auto &[e, w] : adj[u]) {
if (e == pu) continue;
depth[e] = depth[u] + 1;
up[0][e] = {u, w};
FOR(i, 1, 20) {
auto [nxt, d] = up[i - 1][e];
up[i][e].fi = up[i - 1][nxt].fi;
up[i][e].se = up[i - 1][nxt].se + d;
}
init(e, u);
sub[u] += sub[e];
}
}
ll dist(int u, int v) { // u is a descendant
int d = depth[u] - depth[v];
ll res = 0;
R0F(i, 20) {
if (d & (1 << i)) {
res += up[i][u].se;
u = up[i][u].fi;
}
}
return res;
}
void dfs(int u, int pu, bool keep) {
int mx = 0, big = -1;
int dd = 0;
for (auto &[e, w] : adj[u]) {
if (e == pu) continue;
if (ckmax(mx, sub[e])) big = e, dd = w;
}
for (auto &[e, w] : adj[u]) {
if (e == pu || e == big) continue;
dfs(e, u, 0);
}
if (big != -1) {
dfs(big, u, 1);
shift += dd;
swap(v[u], v[big]);
extra++;
}
v[u].pb(u);
if (cnt.count(targ - shift)) ckmin(ans, cnt[targ - shift] + extra);
ckmin(cnt[-shift], -extra);
for (auto &[e, w] : adj[u]) {
if (e == pu || e == big) continue;
for (auto &x : v[e]) {
v[u].pb(x);
ll y = dist(x, u);
if (cnt.count(targ - y - shift)) ckmin(ans, cnt[targ - y - shift] + depth[x] - depth[u] + extra);
}
for (auto &x : v[e]) {
ll y = dist(x, u);
if (cnt.count(y - shift)) ckmin(cnt[y - shift], -extra + depth[x] - depth[u]);
else cnt[y - shift] = -extra + depth[x] - depth[u];
}
v[e].clear();
}
if (!keep) cnt.clear(), extra = shift = 0;
}
int best_path(int N, int K, int H[][2], int L[]) {
targ = K;
FOR(i, 0, N - 1) {
auto u = H[i][0];
auto vv = H[i][1];
adj[u].pb({vv, L[i]});
adj[vv].pb({u, L[i]});
}
init(0, -1);
dfs(0, -1, 0);
return (ans == INF ? -1 : ans);
}
// void solve()
// {
// int n, k;
// cin >> n >> k;
// int h[n - 1][2];
// int l[n - 1];
// F0R(i, n - 1) cin >> h[i][0] >> h[i][1];
// F0R(i, n - 1) cin >> l[i];
// cout << best_path(n, k, h, l) << '\n';
// }
//
// int main()
// {
// cin.tie(0)->sync_with_stdio(0);
// cin.exceptions(cin.failbit);
// int testcase=1;
// // cin >> testcase;
// while (testcase--)
// {
// solve();
// }
// }
