#include<bits/stdc++.h>
using namespace std;
const int N=5e5+10;
vector<pair<int,int>>G[N];
int d[N], dis, h[N], fa, f[N], v[N]; 
void dfs1(int x)
{
	v[x]=1;
	for(auto i:G[x])
	{
		int y=i.first,c=i.second; if(v[y]==1) continue;
		d[y]=d[x]+c; f[y]=x;
		if(dis<d[y]) dis=d[y], fa=y;
		dfs1(y);
	}
}
void dfs2(int x)
{
	v[x]=1;
	for(auto i:G[x])
	{
		int y=i.first,c=i.second; if(v[y]==1) continue;
		dfs2(y);
		h[x]=max(h[x], h[y]+c); 
	}
}
int main()
{
	int n,S; scanf("%d%d", &n, &S);
	for(int i=1,x,y,c; i<n; i++)
	{
		scanf("%d%d%d", &x, &y, &c);
		G[x].push_back({y,c}); G[y].push_back({x,c});
	}
	int l, r; 
	memset(v, 0, sizeof(v)); 
	d[1]=0;f[1]=0; dis=0; dfs1(1); l=fa;
	memset(v, 0, sizeof(v)); 
	d[l]=0;f[l]=0; dis=0; dfs1(l); r=fa;
	
	memset(v, 0, sizeof(v));
	memset(h, 0, sizeof(h));
	for(int i=r; i; i=f[i]) v[i]=1;
	int maxh=0; 
	for(int i=r; i; i=f[i]) dfs2(i), maxh=max(maxh, h[i]);
	
	int ans=(1LL<<31)-1;
	for(int i=r, j=r; i; i=f[i])
	{
		while(d[j]-d[i]>S) j=f[j];
		ans=min(ans, max({maxh, d[i]-d[l], d[r]-d[j]}));
	}
	printf("%d\n", ans);
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
const int N=5e5+10;
vector<pair<int,int>>G[N];
int d[N], dis, h[N], fa, f[N]; bool v[N]; 
void dfs1(int x)
{
	v[x]=1;
	for(auto i:G[x])
	{
		int y=i.first,c=i.second; if(v[y]==1) continue;
		d[y]=d[x]+c; f[y]=x;
		if(dis<d[y]) dis=d[y], fa=y;
		dfs1(y);
	}
}
void dfs2(int x)
{
	v[x]=1;
	for(auto i:G[x])
	{
		int y=i.first,c=i.second; if(v[y]==1) continue;
		dfs2(y);
		h[x]=max(h[x], h[y]+c); 
	}
}
int main()
{
	int n,S; scanf("%d%d", &n, &S);
	for(int i=1,x,y,c; i<n; i++)
	{
		scanf("%d%d%d", &x, &y, &c);
		G[x].push_back({y,c}); G[y].push_back({x,c});
	}
	int l, r; 
	memset(v, 0, sizeof(v)); 
	d[1]=0;f[1]=0; dis=0; dfs1(1); l=fa;
	memset(v, 0, sizeof(v)); 
	d[l]=0;f[l]=0; dis=0; dfs1(l); r=fa;
	
	memset(v, 0, sizeof(v));
	memset(h, 0, sizeof(h));
	for(int i=r; i; i=f[i]) v[i]=1;
	int maxh=0; 
	for(int i=r; i; i=f[i]) dfs2(i), maxh=max(maxh, h[i]);
	
	int ans=(1LL<<31)-1;
	for(int i=r, j=r; i; i=f[i])
	{
		while(d[j]-d[i]>S) j=f[j];
		ans=min(ans, max({maxh, d[i]-d[l], d[r]-d[j]}));
	}
	printf("%d\n", ans);
	return 0;
}