#include<bits/stdc++.h>
#define int long long
using namespace std;
int N, K, total=1e14;
vector<pair<int, int> > edge[1000010];
int h[1000010];
int siz[1000010];
int wei[1000010];
map<int, int> sav;
void PDF(int n, int cha){
siz[n]=1;
for(auto gg:edge[n]){
int v=gg.first;
int w=gg.second;
if(v==cha) continue;
h[v]=h[n]+1;
wei[v]=wei[n]+w;
PDF(v, n);
siz[n]+=siz[v];
}
}
void get(int n, int cha, int st){
if(wei[n]-2*wei[st]<=K){
int req=K-(wei[n]-2*wei[st]);
if(sav[req]==0) sav[req]=1e14;
total=min(total, h[n]-h[st]+sav[req]-h[st]);
}
for(auto v:edge[n]){
if(v.first==cha) continue;
get(v.first, n, st);
}
}
void add(int n, int cha, int val, int st){
if(sav[wei[n]]==0) sav[wei[n]]=1e14;
sav[wei[n]]=min(sav[wei[n]], h[n]);
for(auto gg:edge[n]){
int v=gg.first;
if(v==cha) continue;
add(v, n, val, st);
}
}
void DFS(int n, int cha, bool keep){
int found=0;
for(auto gg:edge[n]){
int v=gg.first;
if(v==cha) continue;
if(found==0 || siz[v]>siz[found]) found=v;
}
for(auto gg:edge[n]){
int v=gg.first;
if(v==cha || v==found) continue;
DFS(v, n, 0);
}
if(found!=0) DFS(found, n, 1);
if(sav[wei[n]]==0) sav[wei[n]]=1e14;
sav[wei[n]]=min(sav[wei[n]], h[n]);
if(sav[wei[n]+K]==0) sav[wei[n]+K]=1e14;
total=min(total, sav[wei[n]+K]-h[n]);
for(auto gg:edge[n]){
int v=gg.first;
if(v==cha || v==found) continue;
get(v, n, n);
add(v, n, 1, n);
}
if(keep==0) add(n, cha, -1, n);
}
signed main(){
// freopen("goat.inp", "r", stdin);
// freopen("goat.out", "w", stdout);
ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
cin>>N>>K; h[1]=1; wei[1]=1;
for(int i=1; i<N; i++){
int x, y, w; cin>>x>>y>>w; x++; y++;
edge[x].push_back(make_pair(y, w));
edge[y].push_back(make_pair(x, w));
}
PDF(1, 1);
DFS(1, 1, 0);
if(total>=2e11){
cout<<"-1"; return 0;
}
cout<<total;
}
Compilation message
/usr/bin/ld: /tmp/ccrsHcME.o: in function `main':
race.cpp:(.text.startup+0x0): multiple definition of `main'; /tmp/ccVumyVC.o:grader.cpp:(.text.startup+0x0): first defined here
/usr/bin/ld: /tmp/ccVumyVC.o: in function `main':
grader.cpp:(.text.startup+0x28): undefined reference to `best_path(int, int, int (*) [2], int*)'
collect2: error: ld returned 1 exit status
