#include <cstdio>
#include <iostream>
#include <vector>
#include <cstring>
#include <queue>
#include <algorithm>
#include <cmath>
#include <limits.h>
using namespace std;
typedef pair<int, int> PII;
const int N = 500001;
int n, ss, dis[N], pre[N], q[N]; 
int head[N], numE = 0;
bool vis[N];
vector<PII> path; 
struct Edge{
    int next, to, dis;
}e[N << 1];
void addEdge(int from, int to, int dis){
    e[++numE].next = head[from];
    e[numE].to = to;
    e[numE].dis = dis;
    head[from] = numE;
}
int inline bfs(int s){
	memset(vis, false, sizeof vis);
	dis[s] = 0; vis[s] = true;
	pre[s] = 0;
	q[0] = s;
    int hh = 0, tt = 0;
	while(hh <= tt){
		int u = q[hh++];
		for(register int i = head[u]; i; i = e[i].next){
			int v = e[i].to;
			if(vis[v]) continue;
			vis[v] = true;
			dis[v] = dis[u] + e[i].dis;
			pre[v] = u;
            q[++tt] = v;
		}
	}
	int k, maxn = -1;
	for(int i = 1; i <= n; i++)
		if(dis[i] > maxn) maxn = dis[i], k = i;
	return k;
}

int inline bfs2(int s){
	int hh = 0, tt = 0, res = 0;
	q[0] = s;
	while(hh <= tt){
		int u = q[hh++];
        res = max(res, dis[u]);
		for(register int i = head[u]; i; i = e[i].next){
			int v = e[i].to;
			if(vis[v]) continue;
			vis[v] = true;
			dis[v] = dis[u] + e[i].dis;
			q[++tt] = v;
		}
	}
	return res;
}
bool check(int m){
	memset(vis, false, sizeof vis);
	memset(dis, 0, sizeof dis);
	int u = 0, v = path.size() - 1;
	while(u + 1 < path.size() && path[u + 1].second <= m) u++;
	while(v && path[path.size() - 1].second - path[v - 1].second <= m) v--;
    if(u > v) return true;
	if(path[v].second - path[u].second > ss) return false;
	

    for(int i = 0; i < path.size(); i++)
        vis[path[i].first] = true;
    for(int i = u; i <= v; i++)
		if(bfs2(path[i].first) > m) return false;
	
	return true; 
}
int main(){
	scanf("%d%d", &n, &ss);
	for(register int i = 1; i < n; i++){
		int u, v, w; scanf("%d%d%d", &u, &v, &w);
		addEdge(u, v, w);
        addEdge(v, u, w);
	}
	int u = bfs(1), v = bfs(u);
	
	while(v != 0){
		path.push_back(make_pair(v, dis[v]));
		v = pre[v];
	}
	
	reverse(path.begin(), path.end());
	
	int l = 0, r = INT_MAX;
	while(l < r){
		int mid = (l + r) >> 1;
		if(check(mid)) r = mid;
		else l = mid + 1;
	}
	printf("%d\n", l);
	return 0;
}