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#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;</vector></algorithm></iostream></cstring></cstdio>

typedef long long LL;
typedef pair <int, int> PII; const int N = 500010,
M = N * 2;

int n, s;
int h[N], e[M], w[M], ne[M], idx;
int q[N], dist[N], pre[N];
vector<pii> path;
bool st[N];</pii>

void add(int a, int b, int c)
{
e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}

void bfs(int start)
{
int hh = 0, tt = 0;
memset(dist, 0x3f, sizeof dist);
memset(pre, -1, sizeof pre);
dist[start] = 0;
q[0] = start;

while (hh <= tt)
{
    int t = q[hh++];
    for (int i = h[t]; ~i; i = ne[i])
    {
        int j = e[i];
        if (dist[j] > dist[t] + w[i])
        {
            pre[j] = t;
            dist[j] = dist[t] + w[i];
            q[++tt] = j;
        }
    }
}

}

int bfs_max_dist(int start)
{
int res = 0;
int hh = 0, tt = 0;
q[0] = start;
while (hh <= tt)
{
int t = q[hh++];
res = max(res, dist[t]);

    for (int i = h[t]; ~i; i = ne[i])
    {
        int j = e[i];
        if (!st[j])
        {
            st[j] = true;
            dist[j] = dist[t] + w[i];
            q[++tt] = j;
        }
    }
}
return res;

}

int get_max()
{
int t = 1;
for (int i = 1; i <= n; i++)
if (dist[t] < dist[i])
t = i;
return t;
}

bool check(int mid)
{
int u = 0, v = path.size() - 1;
while (u + 1 < path.size() && path[u + 1].second <= mid) u++;
while (v - 1 >= 0 && path.back().second - path[v - 1].second <= mid) v--;
if (u > v) return true;
if (path[v].second - path[u].second > s) return false;

memset(st, false, sizeof st);
memset(dist, 0, sizeof dist);
for (auto p: path) st[p.first] = true;

for (int i = u; i <= v; i++)
    if (bfs_max_dist(path[i].first) > mid)
        return false;
return true;

}

int main()
{
scanf("%d%d", &n, &s);
memset(h, -1, sizeof h);
for (int i = 0; i < n - 1; i++)
{
int a, b, c;
scanf("%d%d%d", &a, &b, &c);
add(a, b, c), add(b, a, c);
}

bfs(1);
int u = get_max();
bfs(u);
int v = get_max();
while (v != -1)
{
    path.push_back(
    {
        v, dist[v]
    });
    v = pre[v];
}
reverse(path.begin(), path.end());

int l = 0, r = 2e9;
while (l < r)
{
    int mid = (LL) l + r >> 1;
    if (check(mid)) r = mid;
    else l = mid + 1;
}

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

return 0;

}