#include<bits/stdc++.h>

#define ll long long

#define maxn 300001

#define inf 1000000000

#define setIO(s) freopen(s".in","r",stdin)

using namespace std;

deque<int>Q;

int n,S,edges,k;

int hd[maxn],to[maxn<<1],nex[maxn<<1],val[maxn<<1],dis[maxn],fa[maxn],mark[maxn];

void add(int u,int v,int c)

{

    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v,val[edges]=c;

}

void dfs(int u,int ff)

{

    if(dis[u]>dis[k]) k=u;

    fa[u]=ff;

    for(int i=hd[u];i;i=nex[i])

    {

        int v=to[i];

        if(v==ff || mark[v]) continue;

        dis[v]=dis[u]+val[i],dfs(v,u);

    }

}

int answer[maxn];

map<int,int>pre,back;

int main()

{

    int i,j,x,y;

    // setIO("input");

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

    for(i=1;i<n;++i)

    {

        int a,b,c;

        scanf("%d%d%d",&a,&b,&c);

        add(a,b,c), add(b,a,c);

    }

    dis[1]=0, dfs(1,0);

    x=k, k=0,dis[x]=0,dfs(x,0),y=k;

    //y->x

    for(int i=y;i;i=fa[i])  mark[i]=1,pre[i]=dis[i], back[i]=dis[y]-dis[i];

    int ans=inf,s=y;

    for(int i=y;i;i=fa[i])

    {

        dis[k=0]=0;

        dis[i]=0, dfs(i,fa[i]),answer[i]=dis[k];

        while(!Q.empty()&&pre[Q.front()]-pre[i]>S) Q.pop_front();

        while(!Q.empty()&&answer[i]>=answer[Q.back()]) Q.pop_back();

        while(pre[s]-pre[i]>S) s=fa[s];

        Q.push_back(i);

        int a=answer[Q.front()];

        int b=pre[i];

        int c=back[s];

        ans=min(ans,max(max(a,b),c));

    }

    printf("%d\n",ans);

    return 0;

}