//双指针尺取法O(n)秒杀
#include<bits/stdc++.h>
using  namespace std;
typedef long long ll;
const ll N=1000001;
ll n,m=0,i,j,ans=LONG_LONG_MAX,x,y,z,ma,rt1,rt2,s;
ll e[N],w[N],ne[N],head[N],tot=0;
ll dis[500001],pre[500001]={0},f[500001],a[500001];
bool vis[500001];
void add(ll u,ll v,ll w1)
{
    tot++;
    e[tot]=v;w[tot]=w1;ne[tot]=head[u];head[u]=tot;
}
void dfs(ll x)
{
    vis[x]=1;
    for(ll i=head[x];i!=-1;i=ne[i])
    {
        ll j=e[i];
        if(vis[j]==0)
        {
            dfs(j);
            f[x]=max(f[x],f[j]+w[i]);
        }
    }
}
void bfs(ll x)
{
    queue<ll> q;
    q.push(x);
    while(!q.empty())
    {
        ll u=q.front();
        q.pop();//cout<<u<<" "<<q.size()<<endl;
        for(ll i=head[u];i!=-1;i=ne[i])
        {
            ll j=e[i];//cout<<i<<" ";
            if(dis[j]>dis[u]+w[i]&&vis[j]==0)
            {
                dis[j]=dis[u]+w[i];vis[j]=1;
                pre[j]=u;q.push(j);
            }
        }
    }
//  cout<<"b";
}
int main()
{
//  std::ios::sync_with_stdio(false);万恶之源爆bfs
    memset(head,-1,sizeof head);
    cin>>n>>s;
    for(i=1;i<n;i++)
    {
        cin>>x>>y>>z;
        add(x,y,z);add(y,x,z);
    }
    memset(dis,0x3f,sizeof dis);dis[1]=0;
    memset(vis,0,sizeof vis);vis[1]=1;
    bfs(1);ma=LONG_LONG_MIN;
    for(i=1;i<=n;i++)
        if(dis[i]>ma)
        {
            ma=dis[i];rt1=i;
        }
//  cout<<"a";
    memset(dis,0x3f,sizeof dis);dis[rt1]=0;
    memset(vis,0,sizeof vis);vis[rt1]=1;
    bfs(rt1);ma=LONG_LONG_MIN;//cout<<"c";
    for(i=1;i<=n;i++)
        if(dis[i]>ma)
        {
            ma=dis[i];rt2=i;
        }
    //cout<<"a";
    memset(vis,0,sizeof vis);x=rt2;
    while(x!=rt1)
    {
        vis[x]=1;a[++m]=x;
        x=pre[x];
    }
    a[++m]=rt1;vis[rt1]=1;
    for(i=1;i<=m;i++)dfs(a[i]);//cout<<a[i]<<" "<<v[a[i]]<<endl;//cout<<endl;
    ma=LONG_LONG_MIN;
    for(i=1;i<=m;i++)ma=max(ma,f[a[i]]);//cout<<f[a[i]]<<endl;
    j=m;//cout<<"b";
    for(i=m;i>=1;i--)
    {
        while(j>=1&&dis[a[j]]-dis[a[i]]<=s)j--;
        //cout<<ans<<" "<<max(dis[a[i]],dis[a[1]]-dis[a[j+1]])<<endl;
        ans=min(ans,max(dis[a[i]],dis[a[1]]-dis[a[j+1]]));
    }
    cout<<max(ans,ma);
    return 0;
}
/*
5 46
1 2 5
1 3 15
1 5 6
2 4 28
*/