#include<cstdio>

 #include<cstring>

 #include<iostream>

 #define N 600000

 using namespace std;

 int cnt,n,s,head[N],next[N*],u[N*],v[N*],q[N],h,t,d[N],f[N],mx,rt1,mx1,from[N],zhan[N],tot,mark[N];

 int l,r,ans;

 void jia(int a1,int a2,int a3)

 {

     cnt++;

     next[cnt]=head[a1];

     head[a1]=cnt;

     u[cnt]=a2;

     v[cnt]=a3;

     return;

 }

 bool pan(int a1)

 {

     int L=,R=tot;

     for(;zhan[]-zhan[L]<=a1;L++);

     for(;zhan[R]-zhan[tot]<=a1;R--);

     if(zhan[L-]-zhan[R+]>s)

       return ;

     return ;

 }

 void dfs(int a1)

 {

     h=;

     t=;

     q[t]=a1;

     memset(f,,sizeof(f));

     f[a1]=;

     d[a1]=;

     for(;h<t;)

       {

         h++;

         int p=q[h];

         for(int i=head[p];i;i=next[i])

           if(!f[u[i]])

             {

               if(mark[u[i]])

                  d[u[i]]=d[p];

               else

                  d[u[i]]=d[p]+v[i];

               q[++t]=u[i];

               from[u[i]]=p;

               f[u[i]]=;

             }

       }

     return;

 }

 int main()

 {

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

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

       {

         int a1,a2,a3;

         scanf("%d%d%d",&a1,&a2,&a3);

         jia(a1,a2,a3);

         jia(a2,a1,a3);

       }

     dfs();

     mx=;

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

       if(mx<d[i])

         {

             mx=d[i];

             rt1=i;

         }

     dfs(rt1);

     mx=;

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

       if(mx<d[i])

         {

             mx=d[i];

             mx1=i;

         }

     r=d[mx1];

     zhan[++tot]=d[mx1];

     mark[mx1]=;

     for(;mx1!=rt1;)

       {

         mx1=from[mx1];

         zhan[++tot]=d[mx1];

         mark[mx1]=;

       }

     dfs(rt1);

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

       if(d[i]>l)

         l=d[i];

     for(;l<=r;)

       {

         int mid=(l+r)>>;

         if(pan(mid))

           {

             ans=mid;

             r=mid-;

           }

         else

           l=mid+;

       }

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

     return ;

 }