#include<cstdio>
#include<algorithm>
using namespace std;
int cnt,n,K,ans,N,root,F_top,last[1000005],sz[1000005],F_[1000005],vis[1000005],F_stack[1000005],G_stack[1000005],F[1000005],G[1000005];
struct node{int to,next,val;
}e[1000005];
void add(int a,int b,int c){e[++cnt].to=b;e[cnt].next=last[a];e[cnt].val=c;last[a]=cnt;
}
void find_root(int x,int fa){sz[x]=1,F_[x]=0;for (int i=last[x]; i; i=e[i].next){int V=e[i].to;if (V==fa || vis[V]) continue;find_root(V,x);sz[x]+=sz[V];F_[x]=max(F_[x],sz[V]);}F_[x]=max(F_[x],N-sz[x]);if (F_[x]<F_[root]) root=x;
}
void get_dis(int x,int fa,int val,int dep){sz[x]=1;if (val==K) ans=min(ans,dep);if (val<=K) F_stack[++F_top]=val;if (val<=K) F[val]=min(F[val],dep);for (int i=last[x]; i; i=e[i].next){int V=e[i].to;if (vis[V] || V==fa) continue;get_dis(V,x,val+e[i].val,dep+1);sz[x]+=sz[V];}
}
void solve(int x){int G_top=0;for (int i=last[x]; i; i=e[i].next){int V=e[i].to;if (vis[V]) continue;F_top=0;get_dis(V,x,e[i].val,1);for (int j=1; j<=F_top; j++) ans=min(ans,F[F_stack[j]]+G[K-F_stack[j]]);for (int j=1; j<=F_top; j++) G[F_stack[j]]=min(G[F_stack[j]],F[F_stack[j]]),F[F_stack[j]]=1e9,G_stack[++G_top]=F_stack[j];}for (int i=1; i<=G_top; i++) G[G_stack[i]]=1e9;
}
void divide(int x){vis[x]=1;solve(x);for (int i=last[x]; i; i=e[i].next){int V=e[i].to;if (vis[V]) continue;N=sz[V],root=0;find_root(V,x);divide(root);}
}
int main(){scanf("%d%d",&n,&K);for (int i=1; i<n; i++){int x,y,z;scanf("%d%d%d",&x,&y,&z);x++,y++;add(x,y,z);add(y,x,z);}for (int i=1; i<=K; i++) F[i]=G[i]=1e9;ans=1e9;N=n,root=0;F_[0]=1e9;find_root(1,0);divide(root);if (ans!=1e9) printf("%d\n",ans);else printf("-1\n");return 0;
}