#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pair<int,int>> vpi;
#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 trav(a,x) for (auto& a: x)
#define pb push_back
#define rsz resize
#define sz(x) int(x.size())
#define all(x) begin(x), end(x)
#define fi first
#define se second
// subtask 1,2,3
int const n=2e5;
unordered_map<int,int> adj[n];
int sub[n];
int const INF=1e9;
int mn=INF;
int k;
int getsub(int now, int par)
{
sub[now]=1;
trav(chi,adj[now])
{
if(chi.fi==par)continue;
sub[now]+=getsub(chi.fi,now);
}
return sub[now];
}
int centroid(int now, int par, int siz)
{
trav(chi,adj[now])
{
if(chi.fi==par)continue;
if(sub[chi.fi]>siz/2)return centroid(chi.fi,now,siz);
}
return now;
}
int const k_=1e6+3;
pair<pii,pii> path[k_];
vi pos;
bitset<k_> got;
void dfs(int now, int par, int cur, int id, int dep)
{
if(cur>k)return;
if(!got[cur])
{
pos.pb(cur);
got[cur]=1;
path[cur] = {{-1,INF},{-1,INF}};
}
if(path[cur].fi.fi==id)
{
path[cur].fi.se = min(path[cur].fi.se,dep);
}
else if(path[cur].se.fi==id)
{
path[cur].se.se = min(path[cur].se.se,dep);
if(path[cur].se.se < path[cur].fi.se)
{
swap(path[cur].se, path[cur].fi);
}
}
else if(dep < path[cur].fi.se)
{
path[cur].se = path[cur].fi;
path[cur].fi = {id,dep};
}
else if(dep < path[cur].se.se)
{
path[cur].se = {id,dep};
}
trav(chi,adj[now])
{
if(chi.fi==par)continue;
dfs(chi.fi,now,cur+chi.se,id,dep+1);
}
}
void solve(int now)
{
pos.clear();
trav(chi,adj[now])
{
dfs(chi.fi,now,chi.se,chi.fi,1);
}
pos.pb(0);
path[0].fi={now,0};
got[0]=1;
trav(i,pos)
{
if(i>k/2)break;
if(!got[k-i])continue;
if(path[i].fi.fi==path[k-i].fi.fi)
{
if(path[i].se.fi!=-1)
{
mn=min(mn,path[i].se.se+path[k-i].fi.se);
}
if(path[k-i].se.fi!=-1)
{
mn=min(mn,path[i].fi.se+path[k-i].se.se);
}
}
else
{
mn=min(mn,path[i].fi.se+path[k-i].fi.se);
}
}
trav(e,pos)
{
got[e]=0;
}
}
void decomp(int now)
{
int siz = getsub(now,-1);
int u = centroid(now,-1,siz);
solve(u);
trav(chi,adj[u])
{
adj[chi.fi].erase(u);
decomp(chi.fi);
}
}
int best_path(int N, int K, int H[][2], int L[]){
k=K;
F0R(i,N-1)
{
int u = H[i][0];
int v = H[i][1];
adj[u].insert({v,L[i]});
adj[v].insert({u,L[i]});
}
decomp(0);
if(mn==INF)return -1;
return mn;
}
