#include <bits/stdc++.h>
#define IO ios::sync_with_stdio(false);cin.tie(0);
#define debug(x) cerr << #x << " = " << (x) << ' '
#define bug(x) cerr << (x) << ' '
#define endl cerr << '\n'
#define all(v) (v).begin(), (v).end()
#define SZ(v) (ll)(v).size()
#define lowbit(x) (x)&-(x)
#define pb emplace_back
#define F first
#define S second
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
//#define TEST
const int N = 1e5+5;
const int Mxm = 1e6+5;
const int INF = 2e9;
int K, ans = INF, dis[N], dep[N], mxs[N], rt, sz[N], cnt, mn[Mxm], mn2[Mxm];
bool vis[N];
vector<pll> g[N];
vector<int> v, v2;
inline void find_rt(int x, int pre)
{
sz[x] = 1, mxs[x] = 0;
for (auto p : g[x])
{
int v = p.F;
if (vis[v] || v == pre) continue;
find_rt(v, x), sz[x] += sz[v];
mxs[x] = max(mxs[x], sz[v]);
}
mxs[x] = max(mxs[x], cnt - sz[x]);
if (mxs[x] < mxs[rt]) rt = x;
}
inline void push(pll p)
{
if (p.F <= K) v2.pb(p.F);
mn2[p.F] = min(mn2[p.F], (int)p.S);
}
inline void dfs2(int x, int pre)
{
push(pll{dis[x], dep[x]});
for (auto p : g[x])
{
int v = p.F, w = p.S;
if (v == pre || vis[v]) continue;
dis[v] = dis[x] + w, dep[v] = dep[x] + 1;
dfs2(v, x);
}
}
inline void calu(int x)
{
dis[x] = dep[x] = 0;
v.clear(); v.pb(0), mn[0] = 0;
for (auto p : g[x])
{
int v = p.F, w = p.S;
if (vis[v]) continue;
dis[v] = dis[x] + w, dep[v] = dep[x] + 1;
v2.clear(); dfs2(v, x);
for (int d : v2)
{
if (d <= K) ans = min(ans, mn[K-d] + mn2[d]);
}
for (int d : v2)
{
if (d <= K)
{
mn[d] = min(mn[d], mn2[d]);
mn2[d] = INF, ::v.pb(d);
}
}
}
for (int d : v) mn[d] = INF;
}
inline void solve(int x)
{
vis[x] = 1;
calu(x);
for (auto p : g[x])
{
int v = p.F, w = p.S;
if (vis[v]) continue;
cnt = sz[v], mxs[rt = 0] = INF;
find_rt(v, x);
solve(rt);
}
}
#ifndef TEST
int best_path(int n, int _k, int e[][2], int len[])
{
K = _k;
for (int i=0; i < n-1; ++i)
{
int x = e[i][0], y = e[i][1], w = len[i];
++x, ++y;
g[x].pb(y, w), g[y].pb(x, w);
}
cnt = n, mxs[rt = 0] = INF;
for (int i=0; i <= K; ++i) mn[i] = mn2[i] = INF;
find_rt(1, 0);
solve(rt);
ans = (ans == INF)?-1 : ans;
return ans;
}
#else
int main(void)
{ IO
int n, i;
cin >> n >> K;
for (i=0; i < n-1; ++i)
{
int x, y, w; cin >> x >> y >> w, ++x, ++y;
g[x].pb(y, w), g[y].pb(x, w);
}
cnt = n, mxs[rt = 0] = INF;
find_rt(1, 0);
solve(rt);
ans = (ans == INF)?-1 : ans;
cout << ans << '\n';
return 0;
}
#endif
