#include<bits/stdc++.h>
using namespace std;
using I=int;
using Lli=long long int;
using B=bool;
const I N=200000;
const I MAX=1e9;
vector<pair<I,I>>adjs[N];
I sizs[N];
B viss[N];
map<Lli,I>diss;
I res=MAX;
I k;
I dfs1(I a,I p=-1){
sizs[a]=1;
for(auto[b,w]:adjs[a])if(b!=p&&!viss[b])sizs[a]+=dfs1(b,a);
return sizs[a];
}
I dfs2(I a,I siz,I p=-1){
for(auto[b,w]:adjs[a])if(b!=p&&!viss[b]&&sizs[b]*2>siz)return dfs2(b,siz,a);
return a;
}
void dfs4(I a,I p,Lli d,I l){
if(diss.count(k-d))res=min(res,diss[k-d]+l);
for(auto[b,w]:adjs[a])if(b!=p&&!viss[b])dfs4(b,a,d+w,l+1);
}
void dfs5(I a,I p,Lli d,I l){
if(!diss.count(d))diss[d]=MAX;
diss[d]=min(diss[d],l);
for(auto[b,w]:adjs[a])if(b!=p&&!viss[b])dfs5(b,a,d+w,l+1);
}
void dfs3(I a){
a=dfs2(a,dfs1(a));
viss[a]=1;
diss.clear();
diss[0]=0;
for(auto[b,w]:adjs[a])if(!viss[b])dfs4(b,a,w,1),dfs5(b,a,w,1);
for(auto[b,w]:adjs[a])if(!viss[b])dfs3(b);
}
I best_path(I n,I t,I h_arr[][2],I l_arr[]){
k=t;
for(I i=0;i<n-1;i++){
I a=h_arr[i][0],b=h_arr[i][1],l=l_arr[i];
adjs[a].push_back({b,l});
adjs[b].push_back({a,l});
}
dfs3(0);
return res==MAX?-1:res;
}
#ifdef ETHANKIM8683
I main(){
cin.tie(0)->sync_with_stdio(0);
I n,k;cin>>n>>k;
I h_arr[n-1][2],l_arr[n-1];
for(I i=0;i<n;i++)cin>>h_arr[i][0]>>h_arr[i][1]>>l_arr[i];
printf("%i\n",best_path(n,k,h_arr,l_arr));
}
#endif
