#include<cstdio>
#include<algorithm>
#include<vector>
#include<map>
#define S 200007
using namespace std;
vector < pair < int , int > > V[S];
int roz[S];
bool deleted[S];
void DFS(int x, int r){
roz[x] = 1;
for(int i = 0 ; i < V[x].size();i++){
if(V[x][i].first != r && !deleted[V[x][i].first]){
DFS(V[x][i].first,x);
roz[x] += roz[V[x][i].first];
}
}
}
int Find(int x){
for(int i = 0 ; i < V[x].size();i++){
if(!deleted[V[x][i].first]){
if(roz[V[x][i].first] > roz[x]/2){
roz[x] -= roz[V[x][i].first];
roz[V[x][i].first] += roz[x];
return Find(V[x][i].first);
}
}
}
return x;
}
long long dp[S];
int l = 0;
int L[S];
int R[S];
int ID[S];
int poz[S];
void DFS2(int x, int r){
L[x] = ++l;
ID[l] = x;
for(int i = 0 ; i < V[x].size();i++){
int v = V[x][i].first;
int c = V[x][i].second;
if(v != r && !deleted[v]){
poz[v] = poz[x] + 1;
dp[v] = dp[x] + c;
DFS2(v,x);
}
}
R[x] = l;
}
long long k;
int odp = 1e9;
map < long long , int > mapa;
void decomposition(int x){
DFS(x,x);
int centroid = Find(x);
poz[centroid] = 0;
dp[centroid] = 0;
DFS2(centroid,centroid);
deleted[centroid] = 1;
for(int i = 0 ; i < V[centroid].size();i++){
int v = V[centroid][i].first;
if(!deleted[v]){
//printf("%d %d %d %d*\n",centroid,v,L[v],R[v]);
for(int j = L[v]; j <= R[v];j++){
int v2 = ID[j];
if(dp[v2] == k){
odp = min(odp,poz[v2]);
//printf("%d %d$\n",centroid,v2);
}
if(mapa[k-dp[v2]]){
odp = min(odp, poz[v2] + mapa[k-dp[v2]]);
//printf("%d %d$$\n",centroid,v2);
}
}
for(int j = L[v]; j <= R[v];j++){
int v2 = ID[j];
if(!mapa[dp[v2]]){
mapa[dp[v2]] = poz[v2];
}else{
mapa[dp[v2]] = min(mapa[dp[v2]],poz[v2]);
}
}
}
}
l = 0;
mapa.clear();
for(int i = 0 ; i < V[centroid].size();i++){
int v = V[centroid][i].first;
if(!deleted[v])
decomposition(v);
}
}
int best_path(int n, int _k, int H[][2], int L[]){
k = _k;
for(int i = 0 ; i < n-1;i++){
V[H[i][0]+1].push_back({H[i][1]+1,L[i]});
V[H[i][1]+1].push_back({H[i][0]+1,L[i]});
}
decomposition(1);
if(odp < 1e8)
return odp;
return -1;
}
/*
int main(void){
int A[10][2] = { {0,1}, {0,2}, {2,3}, {3,4}, {4,5}, {0,6}, {6,7}, {6,8}, {8,9}, {8,10} };
int B[10] = {3,4,5,4,6,3,2,5,6,7};
printf("%d",best_path(11,12,A,B));
return 0;
}
*/
