#include <bits/stdc++.h>
//#include "race.h"
//#include "grader.h"
using namespace std;
#define S second
#define F first
#define LL long long
const int N1 = 2e5+10;
const LL MOD = 1e9+7;
const LL LINF = 1e18;
const LL INF = 1e9;
map<LL,int> *mp[N1];
vector<pair<int,LL>>adj[N1];
LL depth[N1],dis[N1],sizes[N1],in[N1],out[N1],ans[N1];
vector<int>vec;
LL get_mn(LL x,int i){
if((*mp[i]).find(x)!=(*mp[i]).end())
return (*mp[i])[x];
else
return LINF;
}
void update(LL x,LL val,int i){
if((*mp[i]).find(x)!=(*mp[i]).end())
(*mp[i])[x] = min(1ll*(*mp[i])[x],val);
else
(*mp[i])[x] = val;
}
map<LL,int>mp1;
void dfs(int i,int pr,int k){
in[i] = vec.size();
vec.push_back(i);
mp[i] = new map<LL,int>;
sizes[i] = 1;
int heavy = -1;
for(auto x:adj[i]){
if(x.F==pr)continue;
depth[x.F] = depth[i]+1;
dis[x.F] = dis[i]+x.S;
dfs(x.F,i,k);
sizes[i] += sizes[x.F];
if(heavy==-1||sizes[x.F]>sizes[heavy])
heavy = x.F;
}
if(heavy==-1)heavy = i;
mp[i] = mp[heavy];
out[i] = vec.size();
vec.push_back(i);
ans[i] = get_mn(k+dis[i],i)-depth[i];
for(auto x:adj[i]){
int u = x.F;
if(u==pr||u==heavy)continue;
for(int j=in[u];j<=out[u];j++){
int v = vec[j];
ans[i] = min(ans[i],depth[v]+get_mn(k-dis[v]+dis[i]*2,i)-depth[i]*2);
if(dis[v]-dis[i]==k)
ans[i] = min(ans[i],depth[v]-depth[i]);
}
for(int j=in[u];j<=out[u];j++)
update(dis[vec[j]],depth[vec[j]],i);
}
update(dis[i],depth[i],i);
}
int best_path(int N, int K, int H[][2], int L[])
{
int n = N;
for(int i=0;i<n-1;i++){
adj[H[i][0]].push_back({H[i][1],L[i]});
adj[H[i][1]].push_back({H[i][0],L[i]});
}
dfs(0,0,K);
LL ans1 = LINF;
for(int i=0;i<n;i++)
ans1 = min(ans1,ans[i]);
return ans1<n?ans1:-1;
}
/*
#define MAX_N 500000
static int N, K;
static int H[MAX_N][2];
static int L[MAX_N];
static int solution;
inline
void my_assert(int e) {if (!e) abort();}
void read_input()
{
int i;
my_assert(2==scanf("%d %d",&N,&K));
for(i=0; i<N-1; i++)
my_assert(3==scanf("%d %d %d",&H[i][0],&H[i][1],&L[i]));
my_assert(1==scanf("%d",&solution));
}
int main()
{
int ans1;
read_input();
ans1 = best_path(N,K,H,L);
if(ans1==solution)
printf("Correct.\n");
else
printf("Incorrect. Returned %d, Expected %d.\n",ans1,solution);
return 0;
}*/
