#include "race.h"
#include <algorithm>
#include <bitset>
#include <cmath>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <vector>
using namespace std;
template<class T>using pq=priority_queue<T>;
template<class T>using V=vector<T>;
using ll=long long;
using str=string;
using pl=pair<ll,ll>;
using vl=V<ll>;
using vpl=V<pl>;
#define sz(x) ll((x).size())
#define bg(x) begin(x)
#define all(x) bg(x),end(x)
#define sor(x) sort(all(x))
#define ins insert
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ft front()
#define nl "\n"
#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for(ll i=(b)-1;i>=(a);--i)
#define R0F(i,a) ROF(i,0,a)
#define rep(a) F0R(_,a)
#define each(a,x) for(auto &a:x)
template<class T>bool ckmin(T &a,const T &b){return b<a?a=b,1:0;}
template<class T>bool ckmax(T &a,const T &b){return a<b?a=b,1:0;}
const int dx[4]{1,0,-1,0},dy[4]{0,1,0,-1};
const ll MOD=1e9+7;
//const int MOD=998244353;
ll bp(ll a,ll b=MOD-2) {
ll r=1;a%=MOD;
while(b){
if(b&1)r=(r*a)%MOD;
a=(a*a)%MOD,b>>=1;
}
return r;
}
///////////////////////////////////////////////////////////
ll n,k,u,v,w;
vpl ad[200005],val;
vl tm(200005),vi(200005);
void dfs1(ll u,ll p=-1){
ll t=1;
each(v,ad[u])if(v.f!=p&&!vi[v.f]){
dfs1(v.f,u);
t+=tm[v.f];
}
tm[u]=t;
}
void dfs2(ll u,ll p=-1,ll d=0,ll pr=0){
each(v,ad[u])if(v.f!=p&&!vi[v.f]){
val.pb({d+v.s,pr+1});
dfs2(v.f,u,d+v.s,pr+1);
}
}
ll cent(ll u){
dfs1(u);
ll c=u,b=-1,a=u,r=-1;
while(true){
each(v,ad[c])if(!vi[v.f]&&v.f!=b&&tm[u]/2<tm[v.f]){
c=v.f;
break;
}
if(a==c)break;
b=a,a=c;
}
val.clear();
val.pb({0,0});
dfs2(c);
sor(val);
for(ll i=0,j=sz(val)-1;i<j;i++){
while(i+1<j&&k<=val[i].f+val[j-1].f)j--;
if(k==val[i].f+val[j].f){
if(r==-1)r=val[i].s+val[j].s;
else ckmin(r,val[i].s+val[j].s);
}
while(i<j&&val[i].f==val[i+1].f)i++;
}
vi[c]=1;
each(v,ad[c])if(!vi[v.f]){
ll t=cent(v.f);
if(r==-1)r=t;
else if(t!=-1)ckmin(r,t);
}
return r;
}
//void solve(){
int best_path(int N,int K,int H[][2],int L[]){
//cin>>n>>k;
n=N,k=K;
F0R(i,n-1){
//cin>>u>>v>>w;
u=H[i][0];
v=H[i][1];
w=L[i];
ad[u].pb({v,w});
ad[v].pb({u,w});
}
return cent(0);
}
/*
int main(){
cin.tie(0)->sync_with_stdio(0);
#ifndef ONLINE_JUDGE
freopen("test.in","r",stdin),freopen("test.out","w",stdout);
#endif
//int TC;cin>>TC;rep(TC)
solve();
return 1<<32;
}*/
