#include <bits/stdc++.h>
using namespace std;
#define rep(i,s,e) for (ll i = s; i <= e; ++i)
#define rrep(i,s,e) for (ll i = s; i >= e; --i)
#define pb push_back
#define fi first
#define se second
typedef long long ll;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<ii> vii;
const ll mxn = 3e5;
ll ans = LLONG_MAX, dep[mxn], hdep[mxn]={}, sz[mxn], bot[mxn], k;
vii neibs[mxn];
map<ll, ll> deep[mxn];
void get_depth (ll u, ll prev) {
sz[u] = 1;
for (ii vd : neibs[u]) {
ll v = vd.fi, d = vd.se;
if (v == prev) continue;
dep[v] = dep[u]+d;
hdep[v] = hdep[u]+1;
get_depth (v, u);
sz[u] += sz[v];
}
}
void dfs (ll u, ll prev) {
ll heavy = -1, ma = 0;
for (ii vd : neibs[u]) {
ll v = vd.fi;
if (v == prev) continue;
dfs (v, u);
if (sz[v] > ma) {
ma = sz[v];
heavy = v;
}
}
if (heavy==-1) {
bot[u] = u;
deep[u][dep[u]] = hdep[u];
return;
}
bot[u] = bot[heavy];
for (ii vd : neibs[u]) {
ll v = vd.fi;
if (v == prev || v == heavy) continue;
for (ii deps : deep[bot[v]]) {
ll real_dep = deps.fi, high_dep = deps.se;
ll need_dep = k+2*dep[u]-real_dep;
if (deep[bot[u]][need_dep]) ans = min(ans, high_dep+deep[bot[u]][need_dep]-2*hdep[u]);
}
for (ii deps : deep[bot[v]]) {
ll real_dep = deps.fi, high_dep = deps.se;
if (!deep[bot[u]][real_dep] || high_dep < deep[bot[u]][real_dep]) deep[bot[u]][real_dep] = high_dep;
}
}
ll need_dep = k+dep[u];
if (deep[bot[u]][need_dep]) ans = min(ans, deep[bot[u]][need_dep]-hdep[u]);
if (!deep[bot[u]][dep[u]] || hdep[u] < deep[bot[u]][dep[u]]) deep[bot[u]][dep[u]] = hdep[u];
}
int best_path (int n, int ok, int h[][2], int l[]) {
k = ok;
rep (i,0,n-2) {
ll a = h[i][0], b = h[i][1], c = l[i];
neibs[a].pb({b,c}), neibs[b].pb({a,c});
}
get_depth(0,-1);
dfs (0, -1);
return (ans==LLONG_MAX?-1:ans);
}
