#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// #include <ext/rope>
using namespace std;
// using namespace __gnu_pbds;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef long double ld;
template <class T>
using VV = vector<vector<T>>;
using VI = vector<int>;
using VVI = vector<vector<int>>;
using VL = vector<long long>;
using VVL = vector<vector<long long>>;
using VC = vector<char>;
using VVC = vector<vector<char>>;
using VB = vector<bool>;
using VVB = vector<vector<bool>>;
using VD = vector<double>;
using VVD = vector<vector<double>>;
using PII = pair<int, int>;
using PLL = pair<long long, long long>;
using PIL = pair<int, long long>;
using PLI = pair<long long, int>;
using VPII = vector<pair<int, int>>;
using VPLL = vector<pair<long long, long long>>;
#define LINE '\n'
#define SPACE ' '
#define PB push_back
#define FOR(i, a, b) for (int i = (a); i < (int(b)); i++)
#define FORE(i, a, b) for (int i = (a); i <= (int)((b)); i++)
#define ALL(x) x.begin(), x.end()
#define RALL(x) x.rbegin(), x.rend()
#define sq(a) ((a) * (a))
#define sz(x) ((int)x.size())
#define fastio() \
ios_base::sync_with_stdio(false); \
cin.tie(nullptr); \
cout.tie(nullptr)
#define debug(x) cerr << #x << " = " << x << endl;
const ll MOD = 1e9 + 7;
template <class T>
inline void maxi(T &a, T b)
{
a = max(a, b);
}
template <class T>
inline void mini(T &a, T b)
{
a = min(a, b);
}
template <class T>
inline void addi(T &a, T b)
{
a = (a + b) % MOD;
}
template <class T>
inline void subi(T &a, T b)
{
a = (a - b + MOD) % MOD;
}
template <class T>
inline T add(T a, T b)
{
return (a + b) % MOD;
}
template <class T>
inline T sub(T a, T b)
{
return (a - b + MOD) % MOD;
}
template <class T>
inline T mul(T a, T b)
{
return ((a % MOD) * (b % MOD)) % MOD;
}
constexpr ll binpow(ll a, ll b, ll mod)
{
ll res = 1;
while (b > 0)
{
if (b & 1)
{
res = (res * a) % mod;
}
a = (a * a) % mod;
b >>= 1;
}
return res;
}
const int INF = 1e9;
const int MAX_N = 2e5 + 3;
VPII g[MAX_N];
int n, k;
ll sum[MAX_N], depth[MAX_N], sz[MAX_N];
map<ll, ll> mp[MAX_N];
ll ans = 1e9;
void dfs(int c, int p) {
depth[c] = depth[p] + 1;
mp[c][sum[c]] = depth[c]; // need it later in dfs2
sz[c] = 1;
for(auto [it, edge] : g[c]) {
if(it == p) continue;
sum[it] = sum[c] + ll(edge);
dfs(it, c);
sz[c] += sz[it];
}
}
void dfs2(int c, int p) {
ll target = k + 2 * sum[c];
for(auto [it, edge] : g[c]) {
if(it == p) continue;
dfs2(it, c);
if(sz(mp[it]) > sz(mp[c])) swap(mp[c], mp[it]);
for(auto [sm, edges] : mp[it]) {
if(mp[c].find(target-sm) != mp[c].end()) {
mini(ans, mp[c][target-sm] + edges);
}
}
for(auto [sm, edges] : mp[it]) {
if(mp[c].find(sm) != mp[c].end()) {
mini(mp[c][sm], edges);
}
else {
mp[c][sm] = edges;
}
}
}
}
int best_path(int N, int K, int H[][2], int L[])
{
if(k == 1) return 0;
n = N;
k = K;
FOR(i, 0, n) {
int u = H[i][0], v = H[i][1];
g[u].PB({v, L[i]});
g[v].PB({u, L[i]});
}
depth[0] = -1;
dfs(0, 0);
dfs2(0, 0);
return ans;
}
