#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define ff first
#define ss second
#define ll int64_t
#define ld long double
#define nl cout<<"\n"
#define all(v) v.begin(),v.end()
#define mset(a,v) memset((a),(v),sizeof(a))
#define forn(i,a,b) for(int64_t i=int64_t(a);i<int64_t(b);++i)
#define forb(i,a,b) for(int64_t i=int64_t(a);i>=int64_t(b);--i)
#define fastio() ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define mod 1'000'000'007
#define mod2 998'244'353
#define inf 1'000'000'000'000'007
#define pi 3.14159265358979323846
template<class key,class cmp=std::less<key>>
using ordered_set=tree<key,null_type,cmp,rb_tree_tag,tree_order_statistics_node_update>;
template<class L,class R> ostream& operator<<(ostream& out,pair<L,R> &p) {return out<<"("<<p.ff<<", "<<p.ss<<")";}
template<class T> ostream& operator<<(ostream& out,vector<T> &v) {out<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())out<<", ";out<<*it;}return out<<"]";}
template<class T> ostream& operator<<(ostream& out,deque<T> &v) {out<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())out<<", ";out<<*it;}return out<<"]";}
template<class T> ostream& operator<<(ostream& out,set<T> &s) {out<<"{";for(auto it=s.begin();it!=s.end();++it){if(it!=s.begin())out<<", ";out<<*it;}return out<<"}";}
template<class T> ostream& operator<<(ostream& out,ordered_set<T> &s) {out<<"{";for(auto it=s.begin();it!=s.end();++it){if(it!=s.begin())out<<", ";out<<*it;}return out<<"}";}
template<class L,class R> ostream& operator<<(ostream& out,map<L,R> &m) {out<<"{";for(auto it=m.begin();it!=m.end();++it){if(it!=m.begin())out<<", ";out<<*it;}return out<<"}";}
void dbg_out() {cerr<<"]\n";}
template<typename Head,typename... Tail>
void dbg_out(Head H,Tail... T) {cerr<<H;if(sizeof...(Tail))cerr<<", ";dbg_out(T...);}
#ifdef LOCAL
#define dbg(...) cerr<<"["<<#__VA_ARGS__<<"] = [",dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif
//---------------------------------mars4---------------------------------
vector<ll> sz;
vector<ll> dist;
vector<ll> depth;
vector<map<ll,ll>> g;
vector<vector<pair<ll,ll>>> v;
ll k;
ll ans=inf;
void dfs_sz(ll cur,ll prev,ll len,ll level)
{
sz[cur]++;
dist[cur]=len;
depth[cur]=level;
for(auto [i,w]:v[cur])
{
if(i!=prev)
{
dfs_sz(i,cur,len+w,level+1);
sz[cur]+=sz[i];
}
}
}
void dfs(ll cur,ll prev)
{
ll bsz=-1;
ll big=-1;
for(auto [i,w]:v[cur])
{
if(i!=prev)
{
if(sz[i]>bsz)
{
bsz=sz[i];
big=i;
}
}
}
for(auto [i,w]:v[cur])
{
if(i!=prev and i!=big)
{
dfs(i,cur);
}
}
if(big!=-1)
{
dfs(big,cur);
swap(g[cur],g[big]);
}
for(auto [i,w]:v[cur])
{
if(i!=prev and i!=big)
{
for(auto [len,d]:g[i])
{
ll req=k-len+2*dist[cur];
if(g[cur].count(req))
{
ans=min(ans,g[cur][req]+d-2*depth[cur]);
}
}
for(auto [len,d]:g[i])
{
if(g[cur].count(len))
{
g[cur][len]=min(g[cur][len],d);
}
else
{
g[cur][len]=d;
}
}
}
}
ll req=dist[cur]+k;
if(g[cur].count(req))
{
ans=min(ans,g[cur][req]-depth[cur]);
}
g[cur][dist[cur]]=depth[cur];
}
int best_path(int N,int K,int H[][2],int L[])
{
k=K;
sz=vector<ll>(N);
dist=vector<ll>(N);
depth=vector<ll>(N);
g=vector<map<ll,ll>>(N);
v=vector<vector<pair<ll,ll>>>(N);
ans=inf;
forn(i,0,N-1)
{
ll l=H[i][0];
ll r=H[i][1];
ll w=L[i];
v[l].push_back({r,w});
v[r].push_back({l,w});
}
dfs_sz(0,-1,0,0);
dfs(0,-1);
if(ans==inf)
{
ans=-1;
}
return ans;
}
