LG4149

#include<bits/stdc++.h>

using namespace std;

#define gc c=getchar()
#define r(x) read(x)
#define ll long long

template<typename T>
inline void read(T&x){
    x=0;T k=1;char gc;
    while(!isdigit(c)){if(c=='-')k=-1;gc;}
    while(isdigit(c)){x=x*10+c-'0';gc;}x*=k;
}

const int N=200005;
const int M=1000005;

int n,m;

int root,SIZE;
int s[N];
int siz[N];

bool vis[N];

int ecnt;
int fir[N],nex[N<<1],to[N<<1],w[N<<1];

inline void addedge(int u,int v,int c){
    nex[++ecnt]=fir[u],fir[u]=ecnt,to[ecnt]=v,w[ecnt]=c;
    nex[++ecnt]=fir[v],fir[v]=ecnt,to[ecnt]=u,w[ecnt]=c;
}

void getroot(int x,int f){
    siz[x]=1;
    s[x]=0;
    for(int i=fir[x];i;i=nex[i]){
        int v=to[i];
        if(v==f||vis[v])continue;
        getroot(v,x);
        siz[x]+=siz[v];
        s[x]=max(s[x],siz[v]);
    }
    s[x]=max(s[x],SIZE-siz[x]);
    if(s[x]<s[root])root=x;
}

int F[M];
int G[M];
int CanF[N],totF;
int CanG[N],totG;

void getdist(int x,int f,int dist,int step){
    if(dist>m)return ;
    if(!F[dist]){
        CanF[++totF]=dist;
        F[dist]=step;
    }
    else if(step<F[dist])F[dist]=step;
    for(int i=fir[x];i;i=nex[i]){
        int v=to[i];
        if(v==f||vis[v])continue;
        getdist(v,x,dist+w[i],step+1);
    }
}

int ans=1e9;

void solve(int x,int size){
    vis[x]=1;
    for(int i=fir[x];i;i=nex[i]){
        int v=to[i];
        if(vis[v])continue;
        getdist(v,x,w[i],1);
        if(F[m])
        ans=min(ans,F[m]);
        for(int i=1;i<=totF;++i){
            if(G[m-CanF[i]])
            ans=min(ans,G[m-CanF[i]]+F[CanF[i]]);
        }
        for(int i=1;i<=totF;++i){
            if(!G[CanF[i]]){
                CanG[++totG]=CanF[i];
                G[CanF[i]]=F[CanF[i]];
            }
            else if(F[CanF[i]]<G[CanF[i]])G[CanF[i]]=F[CanF[i]];
        }
        for(int i=1;i<=totF;++i){
            F[CanF[i]]=0;
        }
        totF=0;
    }
    for(int i=1;i<=totG;++i){
        G[CanG[i]]=0;
    }
    totG=0;
    for(int i=fir[x];i;i=nex[i]){
        int v=to[i];
        if(vis[v])continue;
        s[root=0]=SIZE=(siz[x]<siz[v]?size-siz[x]:siz[v]);
        getroot(v,0);
        solve(root,SIZE);
    }
}

int main(){
//  freopen(".in","r",stdin);
//  freopen(".out","w",stdout);
    r(n),r(m);
    for(int i=1;i<n;++i){
        int u,v,w;
        r(u),r(v),r(w);
        addedge(++u,++v,w);
    }
    s[root=0]=SIZE=n;
    getroot(1,0);
    solve(root,n);
    if(ans==1e9)ans=-1;
    printf("%d\n",ans);
    return 0;
}