#include "race.h"
#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 = 2e5+5;
const int INF = 2e9;
ll K, sum[N], dep[N], ans = INF;
vector<pll> g[N];
inline void dfs0(int x, int pre)
{
for (pll p : g[x])
{
int v = p.F, w = p.S;
if (v == pre) continue;
sum[v] = sum[x] + w, dep[v] = dep[x] + 1;
dfs0(v, x);
}
}
inline void push(map<ll, int> &mp, pll p)
{
if (mp.count(p.F)) mp[p.F] = min(mp[p.F], (int)p.S);
else mp[p.F] = p.S;
}
inline map<ll, int> dfs(int x, int pre)
{
map<ll, int> mp, tmp;
for (pll e : g[x])
{
int v = e.F;
if (v == pre) continue;
tmp = dfs(v, x);
if (SZ(tmp) > SZ(mp)) swap(mp, tmp);
for (auto p : tmp)
{
if (mp.count(K-p.F + sum[x]*2))
ans = min(ans, p.S + mp[K-p.F + sum[x]*2] - dep[x]*2);
}
for (auto p : tmp) push(mp, p);
}
if (mp.count(K + sum[x]))
ans = min(ans, mp[K + sum[x]] - dep[x]);
push(mp, pll{sum[x], dep[x]});
//debug(x), endl;
//for (auto p : mp) debug(p.F), debug(p.S), endl; endl;
return mp;
}
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);
}
dfs0(1, 0);
dfs(1, 0);
ans = (ans == INF)?-1 : ans;
return ans;
}
#ifdef TEST
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);
}
dfs0(1, 0);
dfs(1, 0);
//for (i=1; i <= n; ++i) bug(sum[i]); endl;
//for (i=1; i <= n; ++i) bug(dep[i]); endl;
//debug(ans), endl;
if (ans == INF) cout << "-1\n";
else cout << ans << '\n';
return 0;
}
#endif
