#include<bits/stdc++.h>
#define fo(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
#define Ts template<typename Ty,typename... Ar>
#define Tp template<typename Ty>
#define ll long long
#define RS register
#define gc getchar
#define pc putchar
#define I inline
using namespace std;
Tp I Ty wmax(Ty a,Ty b){return a>=b? a:b;}
Tp I Ty wmin(Ty a,Ty b){return a<=b? a:b;}
namespace WrongIO
{
	Tp I void read(Ty &x){x=0;Ty opt=1;char c=gc();while(!isdigit(c)&&c!='-')c=gc();if(c=='-')opt=-1,c=gc();while(isdigit(c))x=(x<<3)+(x<<1),x+=c-'0',c=gc();x*=opt;return;}
	Tp I void write(Ty x){short OI_USE[50],OI_top=0;if(x<=0) if(x==0)pc('0');else pc('-'),x*=-1;while(x)OI_USE[++OI_top]=x%10,x/=10;while(OI_top--)pc(OI_USE[OI_top+1]+'0');return;}
    I void writec(char c[]){int len=strlen(c);for(int i=0;i<len;i++)pc(c[i]);}
    I void writes(string s){int len=s.length();for(int i=0;i<len;i++)pc(s[i]);}
    I void readc(char &c,int l,int r){c=gc(); while(c!=EOF&&(c<l||c>r)) c=gc();}
    I void readc(char &c,char val){c=gc();while(c!=EOF&&c!=val) c=gc();}
    I void readc(char val){char c;c=gc();while(c!=EOF&&c!=val) c=gc();}
    I void readls(string &s){char c=gc();while(c!='\n') s.push_back(c),c=gc();}
    Ts I void read(Ty &x,Ar &...y) {read(x),read(y...);}
} using namespace WrongIO;
ll n,k,siz[200050],maxp[200050],tg[1000050],vis[200050],sum,rt,ans=1e9;
struct awa{
	ll v,w;
};
vector<awa> vt[200050];
void getrt(ll u,ll lst)
{
	siz[u]=1; maxp[u]=0;
	for(awa tp:vt[u])
	{
		ll v=tp.v; if(v==lst||vis[v]) continue;
		getrt(v,u); siz[u]+=siz[v];
		maxp[u]=wmax(maxp[u],siz[v]);
	} maxp[u]=wmax(sum-siz[u],maxp[u]);
	if(maxp[u]<maxp[rt]) rt=u; return;
}
awa q[200050],p[200050];ll pt,qt;
void dfs(ll u,ll lst,ll vlx,ll len)
{
	//cout<<u<<endl;
	for(awa tp:vt[u])
	{
		ll v=tp.v; if(vis[v]||v==lst) continue;
		if(tp.w+vlx>k) continue;
		q[++qt]=awa{tp.w,len};
		if(tg[k-tp.w-vlx]!=-1) ans=wmin(ans,tg[k-tp.w-vlx]+len);
		dfs(v,u,vlx+tp.w,len+1);
	} return;
} 
void solve(ll u,ll nm)
{
	
	vis[u]=1;
	for(awa tp:vt[u])
	{
		ll v=tp.v; if(vis[v]) continue;
		if(tp.w>k) continue;
		q[++qt]=awa{tp.w,1};
		if(tg[k-tp.w]!=-1) ans=wmin(ans,tg[k-tp.w]+1);
		dfs(v,u,tp.w,2);
		while(qt>=1)
		{
			awa tp=q[qt]; qt--; p[++pt]=tp;
			if(tg[tp.v]==-1) tg[tp.v]=tp.w;
			else tg[tp.v]=wmin(tp.w,tg[tp.v]);
		}
	}
	while(pt>=1) tg[pt]=-1,pt--;
	pt=qt=0;
	for(awa tp:vt[u])
	{
		ll v=tp.v; if(vis[v]) continue;
		if(siz[v]>siz[u]) sum=nm-siz[u]; else sum=siz[v];
		rt=0; getrt(v,0); solve(v,sum);
	} return;
}
int main()
{
	//fo("test");
	//writes("-1"); return 0;
	read(n,k); maxp[0]=1e9; tg[0]=0;
	for(ll i=1;i<=1000000;i++) tg[i]=-1;
	for(ll i=1;i<n;i++)
	{
		ll u,v,w; read(u,v,w); u+=1; v+=1;
		vt[u].push_back(awa{v,w});
		vt[v].push_back(awa{u,w});
	}
	sum=n; getrt(1,0); solve(rt,n);
	if(ans==1e9) writes("-1"); else write(ans);
}

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