1 #include <cmath>
2 #include <cstdio>
3 #include <cstring>
4 #include <cstring>
5 #include <iostream>
6 #include <algorithm>
7 # define maxn 300010
8 using namespace std;
9 void ot(){cout<<"****"<<endl;}
10 int n;
11 int m;
12 struct node{
13 int u,v,w,nxt;
14 }g[2*maxn];
15 int adj[maxn],e;
16 void add(int u,int v,int w){
17 g[e]=(node){u,v,w,adj[u]};
18 adj[u]=e++;
19 }
20 int pre[maxn],dis[maxn];
21 bool vis[maxn],pd[maxn];
22 int q[maxn],head,tail;
23 int st,ed,mx_dis,mn_dis;
24 int lin[maxn],top;
25 void beg(){
26 head=tail=1;
27 q[tail++]=1; vis[1]=1;
28 int mx=0;
29 while(head<tail){
30 int k=q[head++];
31 for(int i=adj[k];i!=-1;i=g[i].nxt){
32 int v=g[i].v; if(vis[v]) continue;
33 dis[v]=dis[k]+g[i].w; vis[v]=1;
34 if(dis[v]>mx) mx=dis[v],st=v;
35 q[tail++]=v;
36 }
37 }
38 memset(vis,0,sizeof(vis));
39 memset(dis,0,sizeof(dis));
40 head=tail=1; mx=0;
41 q[tail++]=st; vis[st]=1;
42 while(head<tail){
43 int k=q[head++];
44 for(int i=adj[k];i!=-1;i=g[i].nxt){
45
46 int v=g[i].v; if(vis[v]) continue;
47 dis[v]=dis[k]+g[i].w; vis[v]=1;
48 pre[v]=k;
49 if(dis[v]>mx) mx=dis[v],ed=v;
50 q[tail++]=v;
51 }
52 }
53 mx_dis=mx;
54 int x=ed;
55 while(x){
56 pd[x]=1; lin[++top]=dis[x];
57 x=pre[x];
58 }
59 memset(vis,0,sizeof(vis));
60 memset(dis,0,sizeof(dis));
61 head=tail=1; mx=0;
62 q[tail++]=ed; vis[ed]=1;
63 while(head<tail){
64 int k=q[head++];
65 for(int i=adj[k];i!=-1;i=g[i].nxt){
66 int v=g[i].v; if(vis[v]) continue;
67 vis[v]=1;
68 if(pd[v]) dis[v]=dis[k];
69 else dis[v]=dis[k]+g[i].w;
70 mx=max(mx,dis[v]);
71 q[tail++]=v;
72 }
73 }
74 mn_dis=mx;
75 }
76 bool check(int x){
77 int l=1,r=top;
78 while(lin[1]-lin[l+1]<=x && l<=top) l++;
79 while(lin[r-1]-lin[top]<=x && r>=1) r--;
80 // cout<<"lr== "<<l<<" "<<r<<endl;
81 // cout<<lin[l]<<" * "<<lin[r]<<endl;
82 return lin[l]-lin[r]<=m?1:0;
83 }
84 int main(){
85 // freopen("a.in","r",stdin);
86 scanf("%d%d",&n,&m);
87 int x,y,z;
88 memset(adj,-1,sizeof(adj));
89 for(int i=1;i<n;i++){
90 scanf("%d%d%d",&x,&y,&z);
91 add(x,y,z); add(y,x,z);
92 }
93 beg();
94 int l=mn_dis,r=mx_dis,mid,ans;
95 // for(int i=1;i<=n;i++) cout<<pd[i]<<" "; cout<<endl;
96 // cout<<"top= "<<top<<endl;
97 // for(int i=1;i<=top;i++) cout<<lin[i]<<" "; cout<<endl;
98 // cout<<check(5)<<endl; exit(0);
99 while(l<=r){
100 mid=(l+r)>>1;
101 if(check(mid)) ans=mid,r=mid-1;
102 else l=mid+1;
103 }
104 cout<<ans<<endl;
105 }
