#include <bits/stdc++.h>

 #define N 200005

 using namespace std;

 int n,m,K,F[N][],H[N],x,y,z,h[N],f[],T,O,e[N],ans,d[N],g[N],t;

 vector <int> a[N],b[N];

 void QH(int x,int fa){

     int y,z=-;

     for (int i=;i<a[x].size();++i)

     if (a[x][i]!=fa){

         QH(y=a[x][i],x);

         for (int j=;j<;++j){

             if (F[y][j]&F[x][j]) z=max(z,j);

             F[x][j]|=F[y][j];

         }

     }

     for (++z;F[x][z];++z);

     F[x][z]=; H[x]=z;

     for (--z;~z;--z) F[x][z]=;

 }

 void dfs(int x,int y,int o){

     if (h[x]>K) return;

     d[++t]=h[x]; g[t]=o; e[++T]=x;

     ans=min(ans,f[K-h[x]]+o);

     for (int i=;i<a[x].size();++i)

     if (H[a[x][i]]<O&&a[x][i]!=y){

         h[a[x][i]]=h[x]+b[x][i];

         dfs(a[x][i],x,o+);

     }

 }

 void go(int x){

     O=H[x]; h[x]=T=;

     for (int i=;i<a[x].size();++i)

     if (H[a[x][i]]<O){

         h[a[x][i]]=h[x]+b[x][i];

         t=; dfs(a[x][i],x,);

         for (int j=;j<=t;++j) f[d[j]]=min(f[d[j]],g[j]);

     }

     for (int i=;i<=T;++i) f[h[e[i]]]=n+;

 }

 int main(){

     scanf("%d%d",&n,&K);

     for (int i=;i<n;++i){

         scanf("%d%d%d",&x,&y,&z);

         ++x; ++y;

         a[x].push_back(y);

         b[x].push_back(z);

         a[y].push_back(x);

         b[y].push_back(z);

     }

     QH(,); ans=n+;

     for (int i=;i<=K;++i) f[i]=n+;

     for (int i=;i<=n;++i) go(i);

     printf("%d\n",ans>n?-:ans);

     return ;

 }